Week 3 Flashcards
Th0
benign, undecided precursor helper T cells
- begin as Th0 when they exit the bone marrow and travel to thymus before differentiating
- Differentiate/divide when correct antigen is brought to them by DC
- Previous experience of DC (conditions in periphery, when it was stimulated, what TLR were engaged, what cytokines/chemokines predominated) determine the Th0’s ultimate progeny
Th1
“hypersensitivity” T cells, urgent destruction of invaders
-Involved in inflammation
Secrete lymphokines: IFNy and IL-2 when activated by APC (DC or macrophages)
-Activate M1 angry macrophages (classical pathway)
IFNy is a lymphokine secreted by _______ and acts to activate ________. These then release ______ and _______.
Th1 cells
M1 macrophages
TNFa and IL-1 cytokines
IL-2 is a lymphokine secreted by _______ and acts to…
Th1 cells
help CTL get fully activated after they recognize antigen
Th2
- Involved in healing via M2 cells (debris removal, scar formation, walling off pathogens that M1 macrophages have failed to kill)
- Appear later in sites of inflammation
- Leave lymph node as Th1, and circulate in blood/lymph until they encounter their antigen in the tissues
- Secretes lymphokines IL-4, IL-5, and IL-13
IL-4, IL-5, and IL-13 are secreted by _______ and act to…
Th2 cells
attract macrophages via M2 alternative activation
Il-4 is chemotactic for _________
eosinophils (parasite killers)
Th17
involved in inflammation, implicated in many autoimmune diseases
- Makes inflammatory lymphokine IL-17
- Activates M1 macrophages as well
Tfh
help B cells differentiate
- Migrate into follicles of the cortex and help B cells that have recognized antigen become activated and differentiate into antibody secreting plasma cells
- Secrete cytokines and by DIRECT contact stimulate B cells to switch from IgM → IgG, IgA, etc.
Treg make transcription factor _________ and secrete ______ and _______. They have phenotype _________.
Foxp3
TGF-B
IL-10
CD4+/CD8+
Treg
suppress activation and function of all other Th cells
Very potent - can suppress 1000 Th cells
Respond specifically to corresponding antigen, but their suppression of other T cells is NOT antigen-specific → any nearby Th is suppressed
CTL
- immune surveillance
- Delivers “lethal hit” to cells telling it to undergo apoptosis → rapid DNA fragmentation and nuclear collapse
- Activated in lymph nodes after contact with antigen-bearing DC
Two pathways CTL can signal cell death:
1) bind _________ on target –> apoptosis
2) secrete ______ containing _______ and ________ –> __________ –> apoptosis
1) Death Receptor Fas (CD95)
2) secrete lytic granules
containing proteases (granzymes) and proteins (perforins)
–> penetration into target cell
CTL are activated by ______ + _______
CTL are converted into memory cells with the help of _______
Th1 and IL-2
IL-21
Memory cells
the small % of CTL left behind
Replace themselves, rapidly differentiate into effector (helper, killer) cells when re-exposed to low antigen concentrations
CD3
- on the surface of virtually all T cells
- Complex of molecules intimately associated with TCR
- T cell binds correct antigen + MHC with its TCR → CD3 transmits actual signal that turns T cell on
CD4
on T helpers
No reliable surface antigens to distinguish Th1 from Th2 (must look at lymphokines they make)
CD8
on CTL
Lymphokine
short range mediators made by LYMPHOCYTE that affects behavior of the same or another cell.
A subset of cytokines.
EX) IL-2, IFNgamma, IL-4, IL-5, IL-10
Chemokine
small short range mediators made by any cell that causes inflammation
EX) MIP-1 to -4, RANTES, CCL28, CXCL16
Cytokine
short range mediators made by any cell that affects behavior of the same or another cell
EX) IL-1, TNFalpha, IL-12.
How do Tfh cells help B cells get activated by antigen and switch Ig class?
6 steps
1) B cell binds epitope specific to B cell receptor
2) Bound molecule is endocytosed and broken down in endocytic vesicle
3) Peptide fragments bind to MHC Class II molecules brought in by other vesicles that fuse with the endosome and MHC-peptide complex moves to surface
4) B cell displays antigen + Class II MHC
5) Correct Tfh comes along and sees its epitope + Class II MHC on B cell → binds and focuses surface interactions and helper lymphokines on B cell
6) → B cell activated and can class switch
NOTE: epitope that T cell “sees” is not the same as the one B cell “saw”
Mitogen
protein that stimulates T cell (and sometimes B cell) division (a kind of lectin)
Mitogen doesn’t actually bind to antigen-binding site on T cell, like an antigen does - binds to CD3 signal transduction domain
- Can activate all T cells at the same time (can lead to cytokine storm!)
- Can be used in lab to make cells divide and specifically activate all helpers and CTL without regard to antigen specificity
Phyohemagglutinin (PHA) and Concanavalin A (Con A)
mitogen
stimulates T cells to divide by binding CD3
(Antibody to CD3 can be a T cell mitogen too)
Pokeweed mitogen (PWM)
mitogen
stimulates both B and T cells (non-specifically) to divide
Antigens are ______ while mitogens are _______
Specific
nonspecific
B cell antigen receptors __________, while T cell antigen receptors ___________
bind antigen directly with surface antibodies (can interact with FREE antigen)
T cells see antigen ONLY when it is complexed with cell-surface MHC molecules
(attention on cell surfaces, NOT free antigen)
T cell receptor structure
Made of 2 chains: alpha and beta (each has 1 common and 1 variable portion)
-each alpha and beta chain has 3 CDRs and a transmembrane domain
(unlike surface Ig where ONLY the heavy chain is trans-membrane domain)
-Genes: Alpha (V, J), Beta (V, D, J)
Antigen presenting cells include (3)
Dendritic Cell
Macrophage
B-cells
Th0 binds to a good APC, then in order for a T cell to be activated and begin proliferating / differentiating it requires 3 signals
1) Signal via TCR-MHC interaction (a certain number of receptors must interact with antigen and a certain number must interact with specific MHC → sufficient interaction for activation)
2) Accessory molecular interactions only provided by true APC, modify, enhance, or diminish activation
3) Cytokines secreted by APC activate, inhibit or modulate T cell activation
MHC restriction
T-cell is antigen specific and MHC restricted
- CTL does not see antigen alone, but only antigen presented to them on the surface of a genetically-identical cell
- MHC antigens are very variable - thousands of alleles in any population
MHC Class I is on surfaces of ________ and recognized by _______. MHC Class I molecules associated best with peptides from ___________
all nucleated cells
recognized by CTL
proteins synthesized WITHIN the cell itself (not taken up by endocytosis)
MHC class II is on surfaces of __________ and recognized by _________
dendritic, macrophage-type cells, B cells, and other APCs
recognized by T helpers
Extrinsic Pathway of T cell Activation (7 steps)
involves antigen from outside the APC
1) Antigen enters body→ infects locally and causes innate response
2) Breakdown products from innate response (or virus itself) ingested by DC
3) Viral proteins → peptides within endosome (broken down by lysozymes)
4) Endosome fuses with other vesicles with Class II MHC molecules embedded in their membrane (facing IN)
5) Some of the peptide associates with the MHC molecule
6) Endosome goes to cell surface and fuses with plasma membrane → MHC + antigenic peptide are exposed to outside world
7) Appropriate T cell (HELPER T’s) recognizes both MHC + antigen → turned on
Epitope that T cell sees is ALWAYS ________
continuous
vs. B cells which can see discontinuous segments on antigen epitope
Intrinsic Pathway of T cell activation (4 steps)
1) Protein made within cell→ chopped up into peptides→ fuses with vesicles containing Class I MHC molecules embedded in membrane
2) Some of the peptide associates with MHC molecules→ fuses with plasma membrane
3) MHC + peptide are exposed to outside world
4) Appropriate T cell (CYTOTOXIC) recognizes both MHC + antigen → turned on
Cross-Presentation
Allows peptides from antigens it’s eaten leak over to “intrinsic” pathway so it can present them on Class I AND Class II MHC at the same time
- Eats it, breaks it down in endosome→ present on class II (extrinsic)
- Eats some stuff, lets it leak out of endosome → presents on class I like it was made inside the cell (intrinsic)
CTL cells typically kill cells infected with ________ because they are activated by _________
viruses
MHC Class I, intrinsic pathway
T-independent antigens
- no T cell help required for antibody response
- Usually have same epitope repeated over and over (rare in proteins, but common in carbohydrates, ie: Streptococcus pneumoniae)
- response to T-independent antigens is almost all IgM without switching (T cells needed to switch from IgM to IgG, IgA or IgE)
If a person is deficient in T cells, they still can make antibody to carbohydrates.
With protein antigen—a little IgM and NO IgG is made without T cell help
A T cell must… (3)
1) Not recognize “self” - not bind so firmly to self structure (MHC alone, or MC loaded with a “self” peptide) that the T cell becomes activated
(This would be autoimmunity)
2) Not recognize free antigen (which is antibody’s job)
3) Recognize antigenic peptide plus self MHC
T cell maturation:
Th0 cells are _____/______ with activated ________ –> rearrange ________
–> _______/_______ –> ____________ –> mature phenotype (_____/_______) or (_______/_______)
CD4-/CD8- (double negative)
activated RAG DNA recombinases –> rearrange TCR V(D)J genes
–> (CD4+/CD8+) double positive
–> selection and turn off one gene
–> mature phenotype (single positive) CD4+/CD8- or CD4-/CD8+
Repertoire selection can be explained by 3 theories
Positive Selection
Negative Selection
Non-selection
Positive selection:
1) Thymocyte TCR encounters MHC (both class I and II) loaded with endogenous self peptides
2) LOW affinity for binding between TCR and MHC, but binds just enough to be told to mature
3) Affinity for SELF MHC, but NOT SELF PEPTIDE → high affinity for self MHC + foreign peptide in periphery
Explains MHC restriction - only recognize specific MHC from that person because they were positively selected for that
Negative Selection
TCR binds MHC bound to SELF peptide with HIGH affinity → activate T cell → cell dies by apoptosis or becomes Treg
Otherwise would result in autoimmunity
AIRE (autoimmune regulatory) gene
causes thymic stromal cells to express stuff that makes sure T cells come into contact with important “self” items → T cells bind → killed
Non selection
Random V(D)J gene segments generated → most resultant TCR has no affinity for particular MHC molecules in thymus → immature cell receives no stimulation through TCR → dies by apoptosis in 2-3 days
Major Histocombatibility Complex (MHC)
- family of genes, coded for on a single chromosome (chr 6)
- very high degree of allelic variability
HLA = human MHC
Class I MHC include HLA-__ and HLA-___.
These are on ______ cells and recognized by _____ cells
HLA-A, HLA-B
on ALL nucleated cells (and platelets)
recognized by cytotoxic killer T cells
Class II MHC include HLA-____.
These are on _______ cells and are recognized by ______ cells
antigen presenting cells only (dendritic, macrophages, B cells, etc.)
recognized by T helper cells
HLA (MHC) structure
Class I vs. Class II
glycoprotein + 2 polypeptide chains
Class I antigens: allelically variable chain + invariant chain (B2-microglobulin)
Class II antigens: two variable (alpha and beta) chains
Syngenic/isografts
grafts between genetically identical individuals
Allogenic/allografts
rafts between non-identical members of the same species
Xenogeneic/Xenografts
grafts between members of different species
Autografts
graft from one individual to himself
Haplotype and MHC genes
set of alleles at a group of linked loci
MHC gene set that you inherited from your parents is called a haplotype.
(Mom has 2 haplotypes, Dad has 2 haplotypes)
No recombination within a haplotype of MHC (linkage disequilibrium)
________ matching is the most important thing for donors because…
HLA-DR (class II)
T helper cells won’t be stimulated.
For Class I matching ______ and ________ are the most important thing because…
HLA-A and HLA-B
killer T cells won’t be stimulated but Th1 cells will be.
Who would be the best donor for someone?
- an identical twin, followed by a sibling, there is a 25% chance that two siblings will have identical haplotypes
- Parents will always be ½ different from their child so they are not good donors
- Children are ½ different from their parents, so they are not good donors.
- You can also use volunteer donor if they match via HLA.
One-way mixed leukocyte reaction (MLR)
- want to see how strongly recipient’s T cells recognize Class II of this potential donor versus that one?
1) WBCs from donor treated (DNA synthesis inhibitors, radiation) to prevent their division - only want to know if recipient can recognize donor’s MHC?
(Lymphocytes of donor killed, monocytes survive)
2) WBCs from donor and recipient are mixed together to see if recipient’s Th cells divide in response to the donor’s HLA-D (mostly DR, on monocytes).
3) Th of one person looking for class II will see class II on monocytes of other person → stimulated, divide, active, release cytokines
A strong reaction (burst of cell division) may preclude the transplant
If you’re immunologically similar then there will be very little reaction
HLA-D vs. HLA-DR -DP -DQ
HLA-D are all Class II MHC
HLA-DR has to do with transplantation
HLA-DQ and HLA-DP have to do more with autoimmune diseases.
If the donor and recipient are identical Class I but different at Class II…
Th1 activated, no CTL activated
Graft rejected slowly
If donor and recipient are different at Class I but identical at Class II…
No Th1 activated (no IL-2 produced), few CTL activated
→ Class II match is the most important thing
Hyperacute Rejection
Graft given to patient who has preexisting antibody (IgG or IgM) to it (either to MLA due to prior graft transfusions or in a mismatch to blood group antigens)
Ab binds endothelial cell of graft blood vessels → complement activated →
Organ may never become perfused with blood (“white graft”)
Graft Rejection: Th 1 cell recognizes foreign HLA-DR on graft cells –>
_______ proliferates (this is what the MLR measures) and secrete lymphokines (______ and _____) to attract a ________ inflammatory response and activate ______
Macrophages produce pro-inflammatory cytokines (_______), CTL active, –> graft is destroyed.
Th1 proliferates
secrete lymphokines (IFNgamma and IL-2)
attract macrophage inflammatory response and activate CTLs
pro-inflammatory cytokines (TNF-alpha)
CTL active –> graft is destroyed.
Graft Rejection: CTL’s recognize foreign HLA-A and HLA-B on all cells
This recognition is insufficient to activate them; they also require Th1-derived interleukins as a 2nd signal.
Once activated the CTL’s become highly cytotoxic
Graft Rejection
Exactly parallels what happens in normal immune response (like a virus) except that in a normal response a peptide + self-MHC is recognized, in rejection its foreign MHC.
T cells selected to recognize _______ but also recognize ________
why?
self MHC + antigen
foreign MHC (allorecognition)
The recognition of foreign MHC is a chance cross-reaction; the receptors are actually selected to recognize self-MHC and antigen
5% of T cells will bind a foreign MHC strong enough to cause activation.
Ankylosing spondylitis
arthritic condition, inflammation of the insertions of tendons into bones→calcification of joints and they become inflexible (ankylosed).
92% of people with this are HLA-B27 (90x greater risk if HLA-B27)
Strong association between HLA-DR3 and –DR4 and ____________
juvenile diabetes
Lymph node function
non-specific filters of debris, microorganisms, etc.
Key site for antigen presentation in adaptive immunity
Primary lymph organs
bone marrow and thymus gland
- Major sites of development of B lymphocytes and T lymphocytes, respectively
- Lymphopoiesis (differentiation of lymph cells from pluripotent progenitors)
Secondary Lymph organs
aggregates of lymphocytes found in close proximity to antigen presenting cells and can also furnish an adaptive immune response
Includes lymph nodes, tonsils, adenoids, Peyer’s patch and spleen
Seeded with cells from primary organs.
Mucosal-Associated Lymphoid tissue (5)
1) Tonsils (palatine, lingual and pharyngeal (adenoids)
2) Esophageal nodules
3) appendix
4) bronchial nodules
5) Large number of aggregations of lymphocytes in intestine
(Usually increase in size / abundance along intestine length until in colon → very abundant multiple groups of nodules both in mucosa and submucosa known as Peyer’s patches)
Distribution of lymph nodes
small organs all over the body, found individually or in chain/clusters
General flow of lymph through node:
1) Lymphocytes enter in via afferent lymphatic vessels
2) –> small lymphatic vessels lined with thin squamous endothelium
3) Lymphocytes enter node into the subcapsular space
4) Lymph fluid and lymphocytes leave node via efferent lymphatic vessels
Lymph Node Outer Cortex:
contains (2)
Lymphoid follicles (with germinal centers)
T cells
Lymph node germinal centers contain 6 types of cells and are located in the ______
1) Follicular center cells
2) Centroblasts
3) Centrocytes → plasma cells
1-3 = B cell clones at different stages of cell development
4) Tingible body macrophages (eat lymphocytes that are apoptotic)
5) Follicular dendritic cell
6) T follicular helper cell
Located in lymph node outer cortex
Mantle zone –> Marginal zone in lymph node
Zones of germinal center in lymph node outer cortex
get less densely packed lymphocytes as you move out of germinal center
Center stains lighter because of increased cytoplasm
Lymph Node paracortical region
Mostly T cells, but some B cells
Lymph Node medulla
Region of loosely arranged cords of cells (B, T, and plasma cells)
Lymphatic fluid flows between the cords
Lymph node subcapsular space
Contains macrophages that engulf bacteria and other particles
Lymph node reticular fibers
Cells (especially macrophages) hang on to these as lymph flows past - required due to net flow in lymph nodes
Lymph node blood supply enters through ______ and leaves via _____.
Artery branches repeatedly to supply entire node with O2 and nutrients.
In nodes, vessels are lined by ___________ to allow for _______ and ________
small artery at hilus and leaves via small vein
HIGH ENDOTHELIAL VENULE
to allow for recognition (receptors) and diapedesis of lymphocytes from blood into lymphatic space of node
Blood-Thymus barrier
Endothelial cells of vessels have tight junctions and surrounded by connective tissue ensheathed by endothelioreticular cells.
- Maturing thymocytes NOT exposed to molecules circulating in blood.
- Stromal cells protect them from exposure to antigens and provide conditions for maturation and selection.
Blood flow through thymus
Small arteries enter thymus through outer capsule and penetrate the thymus and bifurcate within the connective tissue septa and flow between lobules.
Reticuloendothelial cells
- forms blood-thymus barrier so maturing thymocytes aren’t exposed to stuff in the blood
- Involved in selection process (+ and -) for thymocytes as they progress towards medulla
- provide support in thymus
Hassall’s Corpuscles
- in medullary region of thymus
- concentric circular layers of reticular cells
- make thymic stromal lymphoprotein to suppress autoimmune events.
- Produce lymphokines that promote thymocyte maturation into adult T cells.
Function of Thymus
- where thymocyte precursor cells undergo processes that allow release of immunocompetent T-lymphocytes
- Proliferation, differentiation, and selection of T cells
- Environment for + and - selection of thymocytes
- Total lymphocyte mass of thymus decreases thru childhood - around puberty fills with fat cells and connective tissue.
Structure of Thymus gland
- bilobed
- connective tissue capsule + septa (trabeculae) that divide the organ into pseudolobules
Densely packed set of developing thymocytes are located in the ________
CORTEX
More mature thymocyte precursors, lees dense are located in the ______
MEDULLA
Does the thymus have reticular fibers?
NO - no bulk fluid flow
stromal cells provide support
Immunity that results from real life exposure to pathogen
Natural, Active
Longest lasting immunity!
enjoying the products of someone else’s immune response
Natural, passive
immunity from intentional immunization with vaccine, toxoids, or other antigenic preparations
Artificial, active
immune serum or purified antibodies protect patient at risk from a particular disease
Artificial, passive
Role of local immunity in response to viruses
Local Immunity: on the surface that is being invaded, can prevent the invasion
Secretion of IgA
Role of humoral immunity in response to viruses
- next line of defense when virus is in plasma phase
- Ab prevents a virus from ever establishing an infection in host
Humoral immunity may prevent viral illness, but once ill, T cell immunity is necessary for recovery
Role of cell mediated immunity in response to viruses
- no antibody → virus infects cells and can alter function or kill them
- Once infection has taken place, necessary to kill infected cells before virus can multiply within them → T cell response
- Viruses that never appear in blood or go latent are hard for the immune system to deal with
Extracellular bacteria are combated principally by ______. How?
antibody (Humoral immunity)
IgA blocks attachment to mucous membranes, and opsonized by plasma antibody and complement
________ is most susceptible to lysis by C9
Neisseria
Intracellular bacterial are combated principally by ________
Cell-mediated immunity
(survive in macrophages
Killed if macrophage activated by Th1 cells)
Toxoid
-can be human or animal antitoxin
-EX) Tetanus, Diptheria
Protection good for 10-20 years
- No side effects, cheap
- Antibodies made against toxoid protect against toxin
Live virus vaccine
infectious, but attenuated (immunogenic but not pathogenic)
Provides better immunity that killed preparations
Adjuvant
substance added to vaccines to make them more immunogenic
Stimulate an innate immune response → more effective adaptive response
Adjuvant + small amount of antigen can make immunity as effective as large amount of antigen
DNA vaccine
advantages and disadvantages
- area of investigation
- Immunization with the DNA that codes for antigen
Advantage:
1) speed (could be available in weeks)
2) DNA more stable than protein or live virus (remote access)
3) produces almost-natural, active immunity because DNA expressed by body cells
Disadvantage:
1) DNA expressed by body cells → CTL activation ending immunity and causing serious damage (autoimmunity)
Babies infected in utero would make _______ anti-rubella –> indicative of _______
IgM
congenital rubella
Babies will have high IgG to rubella because…
mothers will have had natural rubella or been immunized (hopefully)
Conjugate vaccine
- Major immunogens for Hemophilus, Streptococcus, and Neissera are in their capsular carbohydrates
- Carbohydrate response is T-INDEPENDENT response → mostly IgM
- IgM can’t penetrate tissues → insufficient immunity if only vaccinated to this
- Carb coupled to protein antigenic “carrier” to which Tfh cells could respond → help B cells respond to attached carbohydrate → IgG response
Highly effective in babies (and elderly)
Oral polio vaccine
Sabin
- attenuated, live oral vaccine
- Effective via local immunity - high levels of IgA in their secretions → prevent colonization by the real virus
- Not currently used in USA (discontinued 2000) because no more sources of wild-type virus
Parenteral polio vaccine
Salk, killed, injected vaccine
Induces good levels of viral ab in serum
Herd immunity
-proportion of population that has immunity against particular infection
Chance susceptible (non-immune) member of herd contacts infectious member
Chance that if such contact occurs, disease will be transmitted (e.g infectivity of disease organism)
Need lower % herd immunity if diseases is less infectious
Herd effect
decrease in infection rate in the nonimmune part of the herd
Neutrophils stimulated by ______ and ______.
GM-CSF and G-CSF
Neutrophil development
10-14 days in marrow storage pool
Mitotic pool = myeloid precursors (myeloblast, promyelocyte, myelocyte)
Storage pool = Myeloid precursors (metamyelocyte, band, seg)
KEY for fast mobilization of infection - most severe types of neutropenia
Marginating Pool = Released into peripheral blood → circulates for 6 hours → into tissues → turn over in 1-2 days
Neutrophil function
Major component of innate immune system
Migrate quickly to site of infection, ingest and kill microbes
First responder
Important in stimulating wound healing and tissue repair
Nonspecific defense against microbes
Eosinophils appearance
Larger than neutrophil
red-orange granules
bi-lobed nucleus
Eosinophils stimulated by _____
IL-5
Eosinophil development
Made in marrow, released into peripheral blood, move to external surfaces
Survive for weeks in mucosal surfaces
Eosinophil function
Allergic reactions, parasitic infections, response to tumors
Can be phagocytes and immunostimulatory OR immunoinhibitory
Basophil appearance
Similar size to Eosinophils
prominent blue-purple granules
bi-lobed nucleus
Basophils stimulated by ______
IL-3
Basophil development
Produced in marrow, released in peripheral blood, move to tissues (spend most of their life in tissues)
Basophil function
major role in hypersensitivity (allergic) reactions
Receptors for IgE
Monocytes/Macrophages stimulated by ______ and ______
GM-CSF and M-CSF
Monocyte/Macrophage development
7 days (in bone marrow)
Last 3-5 days in intravascular compartment (after last mitotic division)
Macrophages last days-months in tissue
Function of monocytes/macrophages
- migrate from blood to sites of infection
- Provide effector cells to remove microbes, dead and dying inflammatory cells, and debris
- Filter out microbes from blood stream (spleen)
- Process and present antigens to adaptive immune system
- Remove apoptotic cells
Neutropenia:
ANC
decrease in absolute neut count (bands/segs) below accepted norms
Varies with age, race, ethnicity and altitude
ANC
Neutropenia values:
___-___/microL= mild risk for infection
___-____ /microL = moderate to severe risk for infection
1,000 - 500/microL= mild risk for infection
500 - 250 /microL = moderate to severe risk for infection
Neutrophilia
ANC > ______
4 causes
ANC > 7,500 cells/ul
Increased production
Increased release from storage pool
Decreased egress from circulation
Reduced margination
Two ways neutropenia can be classified
1) Marked decrease in bone marrow reserve (primary or secondary)
2) Normal marrow reserve, increased destruction in periphery (usually secondary)
Secondary Neutropenias
1) Chemotherapy drugs
2) Infection associated neutropenia
3) Nutritional deficiencies
4) Aplastic Anemia
5) Drugs
6) Hypersplenism
Infectious neutropenia (viral)
- most common cause of acute neutropenia
- usually acute, resolves in days to months
- suppress BM production or increased turnover
5 mechanisms of infectious associated neutropenia
1) Increased utilization
2) Complement mediated margination
3) BM suppression/failure, direct effect
4) Cytokine/chemokine induced margination
5) Antibody production
Nutritional deficiency neturopenia
- folate, B12, copper, protein/cal deficiency –> ineffective myelopoiesis
- can be associated with other cytopenias and megaloblastic changes in marrow
Aplastic anemia and neutropenia
Stem cell failure
-other cytopenias present (anemia, low platelets)
Chemotherapy and neutropenia
major cause of neutropenia
- direct effect on stem cells of myeloid precursors
- suppression of myelopoiesis
- other cytopenias often present
Drugs can cause neutropenia via 3 mechanisms
1) **Immune (e.g. penicillin, abx) → antibody test positive
2) Toxic (phenothiazine) → directly toxic to cells
3) Hypersensitivity (Dilantin) → rash, fever, lymphadenopathy, etc. (more inflammatory, less directly toxic)
Hypersplenism and neutropenia
-excessive sequestration of neutrophils in spleen
Other cytopenias may be present
Pseudoneutropenia
- infection associated neutropenia
- activation of complement (esp C5) –> demargination of neutrophils
- due to increased turnover of neutrophils
Management of Secondary Neutropenias (6)
1) Withdraw unnecessary drugs and eliminate toxins
2) Treat underlying disorder
3) Replacement of specific deficiency
4) Aggressive management of infections
5) Supportive care including prophylactic abx
6) G-CSF in some conditions (e.g. chemotherapy)
Immune neutropenias
- Antibodies to neutrophils
- Marrow production normal, storage pool normal, increased TURNOVER of neutrophils (vascular compartment decreased)
Categories:
1) Alloimmune (usually in newborn from mom)
2) Chronic benign neutropenia of childhood
3) Autoimmune
4) Drug-induced
Autoimmune Neutropenia
3 clinical features
- Antibody mediated → increased turnover
- May be associated with other autoimmune disorders
Clinical features:
1) Variable ANC
2) Marrow shows normal cellularity
3) Late maturation arrest
Treatment of autoimmune neutropenia (2)
Treat primary autoimmune disorder or hematologic antibodies
G-CSF may be helpful if marrow storage pool depleted
Alloimmune neutropenia
4 clinical features
Maternal alloimmunization to neutrophil-specific antigens (mom ab crosses placenta and binds neonatal neutrophils)
Clinical Features:
1) Neutropenia lasts 2-4 weeks (up to 3-4 months)
2) Can be asymptomatic, or skin infections, rarely pneumonia, sepsis
3) BM shows myeloid hyperplasia
4) Maturation arrest at mature precursors
Treatment of alloimmune neutropenias (3)
Abx, supportive care for infections
IVIG infusions not always effective
Consider G-CSF with severe infection
Congenital Disorders of Stem Cell Myeloid Precursors (3)
1) Kostmann Syndrome
2) Shwachman Diamond Syndrome
3) Cyclic Neutropenia
Kostmann Syndrome
- AD/AR/Sporadic - rare disease
- Apoptosis of myeloid precursors (EARLY - nothing in storage pool)
- ELASTASE gene mutation (ELA-2)
Treatment of Kostmann Syndrome (3)
Aggressive treatment of infections
G-CSF 3-1000 mcg/kg/day to keep ANC > 1000
Consider BMT for poor response to G-CSF
Shwachman Diamond Syndrome
FAS associated apoptosis of marrow precursors
Decrease in CD34+ cells
Marrow stromal defect
AR inheritance
Many have defect in SBDS gene, chr 7
Clinical feautures of Shwachman Diamond Syndrome (7)
1) pancreatic insufficiency
2) fat malabsorption
3) metaphyseal chondroplasia
4) 25% develop aplastic anemia
5) 25% develop MDS/AML
6) Recurrent infection
7) may have associated neutrophil dysfunction
Shwachman Diamond Syndrome treatment (4)
1) Pancreatic enzyme replacement
2) G-CSF
3) Aggressive abx therapy and supportive care
4) BMT for severe complications
Cyclic Neutropenia
- severe peripheral neutropenia for 5-7 days with specific periodicity (12-25 day cycles)
- ELASTASE mutation (different from Kostmann)
- Apoptosis in precursors
- Cyclic hematopoiesis (can cycle platelet and retic count as well)
- AD/AR/sporadic
Treatment of Cyclic Neutropenia (2)
Aggressive abx and supportive care for infection
G-CSF daily or alternate days
Chronic Idiopathic Neutropenia + clinical features + treatment
Myeloid hypoplasia, maturation arrest at myelocyte, metamyelocyte or band stage
Clinical Features:
1) Moderate to severe neutropenia
2) Recurrent infections
3) No other associated findings
4) No neutrophil antibodies detected
Treatment:
Usually responsive to G-CSF
Leukocytosis
-increase in total WBC count beyond normal values.
Main causes: infection, inflammation, nonspecific physiologic stress, or malignancy such as leukemia.
“left shift”: refers to a change in WBC differential that results in an increase in number of segs and bands
Maybe even increase in metamyelocytes and myelocytes (myeloid precursors) which are usually only found in marrow.
Eosinophilia (3 main causes)
absolute count of Eosinophils >350/μl
3 main causes:
1) Allergies or allergic disorders (hay fever, asthma, hives)
2) Parasitic Infections Drug Reactions (usually allergic)
3) Rarer causes = tumors or malignancies, infections like chronic hepatitis
Basophilia
increase in peripheral basophils
Usually seen in drug or food hypersensitivity or uticaria
Seen with infection or inflammation (rheumatoid arthritis, influenza, varicella, smallpox, TB)
Seen in myeloproliferative diseases (CML, myeloid metaplasia)
Monocytosis + 5 main causes
absolute monocyte count > 1,000/ul in newborns and > 500 /ul in children and adults
Main causes:
1) Hematologic (pre) malignancies (AML, Hodgkins)
2) Collagen vascular disease
3) Granulomatous disease (ulcerative colitis, Crohn’s)
4) Infections (TB, pertussis)
5) Carcinoma
Splenic Arterial Blood Flow
Splenic artery –> central arterioles –> discontinuities allow passage of blood, RBCs, platelets, leukocytes into red pulp
Splenic venous blood flow
trabecular vein into splenic vein
White pulp
- more organized lymphoid tissue surrounding central arterioles
- made up of mostly T cells and some B cells
- Purpose is to mount an immunological response to antigens within the blood
Red pulp
- where blood flows through loosely arranged channels/SINUSES
- contains reticular fiber
- where majority of MACROPHAGES reside (remove RBCs, platelets, recycle iron, debris)
Periarteriolar Lymphoid Sheath (PALS)
- bulk of lymphoid tissue (mostly T some B cells) arranged around central arterioles
- Germinal centers are in this sheath
Mucosal Associated Lymphoid tissue includes…
Tonsils (palatine, lingual and pharyngeal (adenoids)
Esophageal nodules
appendix
bronchial nodules
Large number of aggregations of lymphocytes in intestine
(e.g. Peyer’s patches)
Function of spleen
role in adaptive immunity, contains macrophages that remove senescent red cells and platelets, recycle iron, convert hemoglobin to bilirubin
Function of MALT
- associated with mucosal protection
- unencapsulated collections of lymphoid cells and their associated support cells and macrophages
- Contain M (epithelial) cells in SI and respiratory tract
- Deliver antigen to underlying lymphoid tissue and begin adaptive immune response to bad things coming in here
Leukocyte Adhesion Deficiency I associated clinical problems (3)
- Recurrent soft tissue infections (skin, mucous membranes), gingivitis, periodontitis, cellulitis, abscesses.
- Delayed separation of umbilical cord (need neutrophils to infiltrate cord so it can fall off)
- Poor wound healing
Functional/molecular defect in Leukocyte Adhesion Deficiency I
inheritance?
AUTOSOMAL RECESSIVE
- Neutrophilia (cells stuck, can’t get out of circulation to tissues).
- Decreased adherence to endothelial surface → can’t accumulate neutrophils at site of infection / inflammation
- Complete or partial deficiency of CD18 resulting in lack of expression of CD11b/CD18
Chemotactic disorders of neutrophils is caused by defects in…
This causes…
motility due to actin cytoskeleton and directed migration problem
–> ↓chemotaxis, ↓ingestion
Myeloperoxidase deficiency clinical features
Granule defect disorder
- Generally healthy
- Increase fungal infections
- associated with DIABETES
Myeloperoxidase deficiency functional/molecular defect
inheritance?
- Partial or complete deficiency of myeloperoxidase.
- Mild defect in killing bacteria, significant defect in Candida killing
- Post-translational modification defect in processing protein
AR
Chediak-Higashi Syndrome clinical featuers
Granule defect disorder
- Oculocutaneous albinism, nystagmus photophobia
- Recurrent skin/resp tract infections
- Lymphoproliferative phase associated with EBV infection, fever, hepatosplenomegaly and hemophagocytic disorder
- neurodegerative as an adult
Chediak-Higashi Syndrome molecular and functional defects
inheritance?
Neutropenia
- Abnormal degranulation and alterations in membrane fusion –> (giant leaky granules in all leukocytes)
- Metabolic abnormalities in microtubule assembly
- CHS gene identified
- AR
Bactericidal activity/oxygen radical production disorder causes…
-recurrent infections
- Microbes ingested but NOT killed
- no ROS production
- no respiratory burst
Defects in phagocyte function generally characterized by which types of infections (4)
- High rate of bacterial / fungal infection
- Infection with atypical microorganisms
- Peridontal disease in children and infections of exceptional severity
- Recurrent infections in areas of the body that are in contact with the microbial world on the regular
Defects in complement function generally characterized by which types of infections?
C1q, C2, C4 –> ?
C3 –> ?
C5-9 –> ?
C1q, C2, C4 –> SLE, autoimmunity, inflammatory vascular diseases
C3 –> recurrent bacterial infections (pneumococcus, H influenzae)
C5-9 –> increased risk for severe Neisseria bacteria infection (meningitis, arthritis, sepsis)
Describe the NADPH oxidase system
who does it
what does it make
where does it get e-
- usually latent
- with phagocytic stimulus → assembly of cytosolic components with membrane components during RESPIRATORY BURST→ form superoxide anion –> other ROS rapidly formed
-NADPH oxidase = enzyme on cell membrane –> O2 + e- (from NADPH) –> superoxide
Screening tests for phagocytic activity tests for (5)
1) Morphology + CBC
2) Bactericidal activity (ROS presence testing DHR oxidation - higher blue score, the better cell is at making ROS)
3) Chemotaxis assay (actin assemble, response to chemotattractants)
4) Adherence (CD11/CD18, other selectins)
5) Degranulation (ingestion of bacteria, specific granule components)
Screening tests for complement activity (4)
1) measure specific complement components (alternative and classical)
2) Evaluate adaptive immune response
3) Measure IgG level
4) Measure lymphocyte numbers
Treatment for patients with innate immune disorders (5)
1) Anticipate and aggressively treat/define infections (surgery + abx)
2) G-CSF for severe quantitative neutrophelia disorder
3) prophylactic abx or cytokine therapy
4) transplantation of hematopoietic stem cells
5) gene therapy? (still being studied)
Clinical features of Cyclic neutropenia (4)
Recurrent fevers, mouth ulcers with infections during neutropenia
ANC less than 200 for 3-5 days
Bone marrow: myeloid hypoplasia, arrest at myelocyte level during neutropenia
ANC can be normal and pts have no increased infection risk
Chronic Granulomatous disease functional defect
normal adherence, chemotaxis, ingestion, and degranulation
defect in oxidase enzyme system –> NO toxic metabolites produced
Chronic Granulomatous Disease clinical presentation
- recurrent purulent infections with catalase positive bacteria and fungi (external surfaces)
- Deep infections of lungs, spleen, lymph nodes, bones
Clinical features of Kostmann Syndrome (4)
Severe neutropenia (less than 200) early in infancy
Monocytosis, eosinophilia
Marrow: myeloid hyperplasia, severe maturation arrest (promyelocyte/myelocyte stage)
Risk for myelodysplasia or AML
High risk for infection and death before 2 years unless aggressive management
