Immunology - First Aid Flashcards
LN Follicle is the site of…
B-cell localization and proliferation.
In the outer cortex, primary follicles are…
dense and dormant.
Secondary follicles have…
pale central germinal centers.
The LN medulla consists of…
medullary cords (closely packed lymphocytes and plasma cells and medullary sinuses).
Medullary sinuses communicate with…
efferent lympmhatics and contain reticular cells and macrophages.
The LN paracortex houses…
T cells. It is the region of the cortex between the follicles and medulla.
The paracortex contains high endothelial venules through which…
T and B cells enter from the blood.
The paracortex is not well developed in…
pts with DiGeorge syndrome.
The paracortex enlarges in…
an extreme cellular immune response (ex. viral infection).
Cervical LNs drain…
the head and neck.
Hilar LNs drain…
the lungs.
Mediastinal LNs drain…
the trachea and esophagus.
Axillary LNs drain…
the upper limb, breast, and skin above the umbilicus.
Celiac LNs drain…
the liver, stomach, spleen, pancreas and upper duodenum.
Superior mesenteric LNs drain…
the lower duodenum, jejunum, ileum, and colon to the splenic flexure.
Inferior mesenteric LNs drain…
the colon from the splenic flexure to the upper rectum.
Internal iliac LNs drain…
the lower rectum to teh anal canal (above pectinate), bladder, vagina and prostate.
The para-aortic LNs drain…
testes, ovaries, kidneys and uterus.
The superficial inguinal LNs drain…
the anal canal (below pectinate), and skin below the umbilicus (except popliteal).
The popliteal LNs drain…
the dorsolateral foot and posterior calf.
The right lymphatic duct drains…
the right side of the body above the diaphragm.
The thoracic duct drains…
everything else into the junction of the left subclavian and internal jugular veins.
The sinusoids of the spleen are…
long, vascular channels in the red pulp with fenestrated “barrel hoop” basement membrane.
In the spleen, T cells are found in…
the periarterial lymphatic sheath within the white pulp.
In the spleen, B cells are found in…
follicles within the white pulp.
The marginal zone of the spleen is in between the…
red pulp and white pulp, contains APCs and specialized B cells, and is where APCs present blood-borne antigens.
Macrophages in the spleen act to…
remove encapsulated bacteria.
Splenic dysfunction (postsplenectomy, sickle cell) leads to…
decreased IgM which leads to decreased complement activation, which leads to decreased C3b opsonization which leads to increased susceptiblity to encapsulated organisms.
Encapsulated organisms
SHiNE SKis
- Strep pneumo
- H. influenzae
- N. meningitidis
- E. coli
- Salmonella
- Klebsiella
- group B Strep
Postsplenectomy Findings
- Howell-Jolly bodies (nuclear remnants)
- target cells
- thrombocytosis
The thymus is the…
site of T-cell differentiation and maturation. It is encapsulated.
The thymus comes from the…
epithelium of the 3rd pharyngeal pouches. Contains lymphocytes of mesenchymal origin.
The thymus cortex is…
dense with immature T cells.
The thymus medulla is…
pale with mature T cells and Hassall corpuscles containing epithelial reticular cells.
Components of Innate Immunity
- neutrophils
- macrophages
- monocytes
- dendritic cells
- NK cells
- complement
Components of Adaptive immunity
- T cells
- B cells
- circulating antibodies
Innate immunity resistance
- germline encoded
- resistance persists through generations, does not change within an organism’s lifetime
Adaptive immunity resistance
- variation through VDJ recombination during lymphocyte development
- microbial resistance not heritable
Innate immunity response to pathogens
- nonspecific
- occurs rapidly (mins to hrs)
Adaptive immunity response to pathogens
- hihgly specific, refined over time
- develops over long periods; memory response is faster and more robust
Physical barriers of the innate immune resposne
- epithelial tight junctions
- mucus
Innate immunity secreted proteins
lysozyme
complement
CRP
defensins
Adaptive immunity secreted proteins
immunoglobulins
Innate immunity key features in pathogen recognition
-TLRs: pattern recognition receptors that recgonize PAMPs
examples of PAMPs include…
LPS (gram negative bacteria)
flagellin (bacteria)
ssRNA (viruses)
Adaptive immunity key features in pathogen recognition
Memory cells: activated B and T cells; subsequent exposure to a previously encountered antigen leads to a stronger, quicker immune response
MHC is encoded by…
HLA genes and presents antigen fragments to T cells and binds TCRs.
MHC I loci
HLA-A
HLA-B
HLA-C
MHC II loci
HLA-DR
HLA-DP
HLA-DQ
MHC I Binding
TCR and CD8
MHC II Binding
TCR and CD4
MHC I Expression
expressed on all nucleated cells; not expressed on RBCs
MHC II expression
only on APCs
MHC I Function
present endogenously synthesized antigens (viral) to CD8 cytotoxic T cells
MHC II Function
present exogenously synthesized protesin (bacterial proteins, viral capsid proteins) to T helper cells
MHC I Antigen loading
antigen peptides loaded onto MHC I in RER after delivery via TAP peptide transporter
MHC II Antigen loading
antigen loaded following release of invariant chain in an acidified endosome
MHC I mode of transport to cell surface
Beta-2-microglobulin
HLA-A3 association
hemochromatosis
HLA-B27 association
Psoriatic arthritis
Ankylosing spondylitis
arthritis of IBD
Reactive arthritis
HLA-DQ2/DQ8 association
celiac disease
HLA-DR2 association
MS
hay fever
SLE
Goodpasture
HLA-DR3 association
T1DM
SLE
Graves
HLA-DR4 association
Rheumatoid arthritis
T1DM
HLA-DR5 association
Pernicious anemia (leading to B12 deficiency) Hashimoto
NK cells use…
perforin and granzymes to induce apoptosis of virally infected cells and tumor cells.
Activity of NK cells is enhanced by…
IL-2
IL-12
IFN-beta
IFN-alpha
NK cells are induced to kill when exposed to…
a nonspecific activation signal on a target cell and/or to an absence of class I MHC on target cell surface.
NK cells also kill via…
antibody-dependent cell-mediated cytotoxicity (CD16 binds Fc region of bound Ig, activating the NK cell).
Major functions of B cells (3)
- recognize antigen
- produce antibody
- maintain immunologic memory
To recognize antigen, B cells…
undergo somatic hypermutaiton to optimize antigen specificity.
To proudce antibody, B cells differentiate into…
plasma cells to secrete specific Igs.
To maintain immunologic memory, memory B cells…
persist and accelerate future response to Ag.
CD4 T cells function to…
help B cells make antibody and produce cytokines to activate other cells of the immune system.
CD8 T cells function to…
kill virus-infected cells directly.
Other T cell functions
- delayed cell-mediated hypersensitivity (type IV)
- acute and chronic cellular organ rejection
Positive selection occurs in the…
thymic cortex. T cells expressing TCRs capable of binding surface self MHC molecules survive.
Negative selection occurs in the…
medulla. T cells expressing TCRs with high affinity for self antigen undergo apoptosis.
Antigen presenting cells (3)
- B cells
- macrophages
- dendritic cells
Two signals are required for (3):
- T cell activation
- B cell activation
- class switching
Naive T cell activation (4 steps)
- Foreign body is phagocytosed by the dendritic cell.
- Foreign Ag is presented on MHC II and recognized by TCR on Th (helper) cell. Ag is presented on MHC I to Tc (cytotoxic) cells. (signal 1)
- Costimulatory signal is given by interaction of B7 and CD28. (signal 2)
- Th cell activates and produces cytokines. Tc cell activates and is able to recognize/kill virus-infected cells.
B cell activation and class switching (4 steps)
- Helper T cell activation
- B cell receptor-mediated endocytosis; foreing antigen is presented on MHC II and recognized by TCR on Th cell (signal 1).
- CD40 receptor on B cell binds CD40 ligand on Th cell (signal 2).
- Th cell secretes cytokines that determine Ig class switching of B cell. B cell activates and undergoes class switching, affinity maturation, and antibody production.
Th1 cell secretes…
IFN-gamma.
Th1 cell activates…
macrophages and cytotoxic T lymphocytes.
Th1 cell is inhibited by…
IL-4 and IL-10 (from the Th2 cell).
Th2 cell secretes…
IL-4, IL-5, IL-6, and IL-13.
Th2 cell recruits…
eosinophils for parasite defense and promotes IgE production by B cells.
Th2 cell is inhibited by…
IFN-gamma (from the Th1 cell).
Macrophage-lymphocyte interaction
Macrophages release IL-12 which stimulates T cells to differentiate into Th1 cells. Th1 cells release IFN-gamma to stimulate macrophages.
Cytotoxic T cells kill..
virus-infected, neoplastic, and donor graft cells by inducing apoptosis.
Cytotoxic T cells release…
cytotoxic granules containing preformed proteins:
- perforin that helps deliver content of granules into target cell
- granzyme B = a serine protease that activates apoptosis inside a target cell
- antimicrobial that induces apoptosis
Regulatory T cells help maintain specific immune tolerance by…
suppressing CD4 and CD8 T-cell effector functions.
Regulatory T cells are identified by expression of…
cell surface markers CD3, CD4, CD25 (alpha chain of IL-2 receptor) and transcription factor FOXP3.
The part of antibody that recognizes antigen is…
variable part of L and H chains.
Fc portion of IgM and IgG acts to…
fix complement.
Heavy chain contributes to…
Fc and Fab fractions.
Light chain contributes to…
Fab fraction only.
Fab is the…
antigen binding fragment.
Fab determines…
the idiotype: it is a unique antigen-binding pocket. Only 1 antigenic specificity is expressed per B cell.
Fc is the…
constant region with a carboxy terminal. It binds complement and has carbohydrate side chains.
Fc region determines…
isotype (IgM, IgD, etc.)
Antibody diversity is generated by (4):
- random recombination of VJ (light chain) or VDJ (heavy chain) genes
- random combination of heavy chains
- somatic hypermutation (following Ag stimulation)
- addition of nucleotides to DNA during recombination by terminal deoxynucleotidyl transferase
Mature lymphocytes express…
IgM and IgD on their surfaces.
Mature B lymphocytes may differentiate in…
germinal centers of LNs by isotype switching (gene rearrangement; mediated by cytokines and CD40 ligand) into plasma cells that secrete IgA, IgE or IgG.
IgG is the main antibody in…
secondary (delayed) response to an antigen. It is the most abundant isotype in the serum.
Actions of IgG
- fixes complement
- crosses placenta to provide infants w/ passive immunity
- opsonizes bacteria
- neutralizes bacterial toxins and viruses
IgA prevents…
attachment of bacteria and viruses to the mucous membranes. It does NOT fix complement.
IgA crosses epithelial cells by…
transyctosis. It is a monomer in circulation and a dimer when secreted.
IgA is the most..
produced antibody overall but is released into secretions (tears, saliva, mucus) and early breast milk (colustrum).
IgA picks up a…
secretory component from epithelial cells before secretion.
IgM is produced in…
the primary (immediate) response to an antigen. It fixes complement but does not cross the placenta.
Antigen receptor for IgM is on…
surface of B cells.
Form of IgM
monomer on B cell or pentamer when secreted; the pentamer shape allows it to efficiently trap free Ags out of tissue while the humoral response evolves.
IgD is found…
on the surface of many B cells and in the serum.
IgE binds…
mast cells and basophils. Has the lowest concentration in serum.
When exposed to an allergen, IgE will..
cross-linke mediating immediate (type I) hypersensitivity through the release of inflammatory mediators such as histamine.
IgE mediates immunity to…
worms by activating eosinophils.
Thymus-independent antigens are…
antigens lacking a peptide component (ex. lipopolysaccharides from gram-negative bacteria).
Thymus-independent antigens cannot be…
presented by MHC to T cells. They are weakly or non-immunogenic.
Vaccines for thymus-independent antigens often require…
boosters. (ex. pneumococcal polysaccharide vaccine).
Thymus-dependent antigens are…
antigens containing a protein component (ex. diphtheria vaccine).
As a result of direct contact between B cells with thymus-dependent antigens and Th cells, there is…
class switching and immunologic memory.
Acute phase reactants are…
factors whose serum concentrations change significantly in response to inflammation.
Acute phase reactants are produced by the…
liver in both acute and chronic inflammatory states.
Acute phase reactants are induced by…
IL-6, IL-1, TNF-alpha and IFN-gamma.
Positive Acute phase reactants
- serum amyloid A
- C-reactive protein
- ferritin
- fibrinogen
- hepcidin
Negative acute phase reactants
- albumin
- transferrin
Serum amyloid A
prolonged elevation can lead to amyloidosis
C-reactive protein
opsonin; fixes complement and facilitates phagocytosis
measured clinically as a sign of ongoing inflammation
Ferritin
binds and sequesters iron to inhibit microbial iron scavenging
Fibrinogen
coagulation factor; promotes endothelial repair; correlates with ESR
Hepcidin
prevents release of iron bound by ferritin leading to anemia of chronic disease
Albumin
reduction during acute phase reaction acts to conserve amino acids for positive reactants
Transferrin is downregulated in the acute phase to be…
internalized by macrophages to sequester iron.
Complement is a system of…
interacting plasma proteins that play a role in innate immunity and inflammation. MAC defends against gram-negative bacteria.