Immunology FA chapter (no pharm) Flashcards
HLA type A3 is associated with what disease?
hemochromatosis
(=excess iron absorption from diet)
Don’t confuse with HLA D3 (assoc’d w/ SLE, T1DM, Graves)
HLA type B27 is associated with what disease?
Psoriatic Arthritis
Ank spondylitis
arthritis of Inflammatory Bowel Disease
Reactive arthritis
(acronym: PAIR)
HLA type DQ2/DQ8 is associated with what disease?
Celiac
(if you have Celiac, you should go to Dairy Queen DQ not McD’s)
HLA type DR2 is associated with what disease?
Mult sclerosis, hay fever, SLE, Goodpasture
HLA type DR3 is associated with what disease?
Type I DM, SLE, Graves
(“I got DR3 and I can’t see”: T1DM -> diabetic retinopathy; Graves -> exopthalmos; SLE -> photosensitivity)
HLA type DR4 is associated with what disease?
Rheumatoid arthritis, Type I DM
(4 walls in a “rheum”)
HLA type DR5 is associated with what disease?
Pernicious anemia –> B12 deficiency
Hashimoto’s thyroiditis
MHC I and II: present antigens to what cells?
Present antigen fragments to T cells and bind TCRs.
MHC I presents what kind of antigens to what cells?
Presents endogenously synthesized antigens (ie viral) to CD8+ cytotoxic T cells
MHC II presents what kind of antigens to what cells?
Presents exogenously synthized proteins (ie bacterial proteins and viral capsid proteins) to CD4+ T helper cells
NK cells: what do they do
use perforin and granzymes to induce apoptosis of virally infected cells and tumor cells.
(only lymphocyte member of the innate/acute immune system)
what cytokines/proteins enhance the activity of NK cells? (5)
IL-2 from all T cells
IL-12 from macrophages & B cells
interferon-α, interferon-β from viral-infected cells
interferon-γ from Th1 cells
NK cells: 3 ways they are induced to kill target cells?
- when exposed to a nonspecific activation signal on target cell
- and/or the absence of MHC I on a target cell surface
- Fc region of a bound Ig binds CD16 on surface of NK & activates it. “antibody-dependent cell-mediated”
(all nucleated cells except RBCs express MHC I)
Major functions of B cells?
- recognize antigens
- undergo somatic hypermutation to optimize antigen specificity
- produce antibody (differentiate -> plasma cells to secrete immunoglobulins)
- maintain immuno memory (memory B cells)
Major functions of T cells?
- CD4+ T cells (HELPER) help B cells make antibody and produce cytokines
- CD8+ T cells (KILLER) kill virus-infected cells directly
- Delayed cell-mediated hypersensitivity (Type IV)
- Acute and chronic cellular organ rejection
for the differentiation of T cells, where does the T cell precursor come from?
Bone marrow
what happens in the thymus in terms of differentiation of T cells?
- T cells that are positive for both CD4+ and CD8+ are separated into groups that are EITHER CD4+ OR CD8+
- Positive selection (cortex)
- Negative selection (medulla)
what is positive selection? where does it occur?
in the Thymic cortex
T cells that express TCRs capable of binding surface self MHC molecules survive.
what is negative selection? where does it occur?
Thymic medulla
T cells expressing TCRs with high affinity for self antigens undergo apoptosis
what happens to CD4+ T cells in the lymph nodes?
differentiate into Th1 cells, Th2 cells, Th17 cells, and Treg cells
(based on the influence of IL-12, IL-4, TGF-beta/IL-6, and TGF-beta)
what does IL-12 do in the lymph node?
induces CD4+ T cells to differentiate into Th1 cells
what does IL-4 do in the lymph node?
influences CD4+ T cells to differentiate into Th2 cells
what does the combination of TGF-beta and IL-16 do in the lymph node?
induces CD4+ T cells to differentiate into Th17 cells
what does TGF-beta do in the lymph node?
induces CD4+ T cells to differentiate into:
Tregs
Th17 cells (if IL-6 is present)
what are the 3 types of antigen-presenting cells?
- B cells
- Macrophages
- Dendritic cells (Langerhans cell in skin = example of dendritic)
Process of activation for CD4+ T cell?
- Foreign body phagocytosed by dendritic cell
- Foreign antigen presented on MHC I and recognized by TCR on T helper cell. (signal 1)
- Costimulatory signal is given by the interaction of B7 and C28 (signal 2)
- Th cell activates and produces cytokines.
Process of activation for CD8+ T cell?
- Foreign body phagocytosed by dendritic cell
- Foreign antigen presented on MHC II and recognized by TCR on T killer cell. (signal 1)
- Costimulatory signal is given by the interaction of B7 and C28 (signal 2)
- Tc cell activates; recognizes & kills virus-infected cells
Process of B cell activation and class switching?
- Helper T cell is activated
- B cell endocytoses foreign antigen; presents it on MHC II. Recognized by TCR on Th cell. (signal 1)
- B cell’s CD40 receptor binds the T cell’s CD40 ligand (signal 2)
- Th cell secretes cytokines. –> determines Ig class switching of the B cell. B cell activates, undergoes class switching, affinity matulration and antibody production.
Th1 cells secrete what? activate what? inhibited by what?
Secrete IFN-gamma & IL-2
Activate macrophages and cytotoxic T cells
Inhibited by IL4 and IL10 (from Th2 cell)
Th2 cells secrete what?
recruits what?
inhibited by what?
secrete IL-4, IL-5, IL-6, IL-13
Recruit eosinophils for parasite defense, and promote IgE production by B cells
Inhibited by IFN-gamma (from Th1 cell)
what is the overall interaction between macrophages and lymphocytes?
Macrophages release IL-12, which stimulates T cells to differentiate into Th1 cells.
Th1 cells release IFN-gamma to stimulate macrophages
what do cytotoxic T cells kill? generally, how do they do it?
Kill virus-infected, neoplastic, and donor graft cells
induce apoptosis by releasing proteins: Perforin, Granzyme, Granulysin
Cytotoxic T cells release cytotoxic granules containing what? what do the components of these granules do?
Cytotoxic granules contain preformed proteins:
- Perforin: helps deliver content of granules into target cell
- Granzyme B: serine protease; activates apoptosis inside target cell
Granulysin: antimicrobial; induces apoptosis
Lymph node: functions?
secondary lymph organ; functions are nonspecific filtration by macrophages, storage of B and T cells, immune response activation
what occurs in the Follicle of the lymph nodes?
B cell localization and proliferation.
located in outer cortex of node.
what are the 2 parts of the LN Medulla?
what does each part contain/do?
Medulla consists of medullary cords and medullary sinuses.
- Medullary cords contain packed lymptocytes and plasma cells.
- Medullary sinuses contain reticular cells and macrophages. Communicate with efferent (outgoing) lymphatics.
What does the Paracortex of LNs do? Where is it located?
Not well developed in what syndrome?
- Houses T cells. Contains high endothelial venules through which T and B cells enter from blood (paracortex = pathway)
- Located between follicles and medulla
- Not well developed in patients with DiGeorge syndrome
during an extreme cellular immune response such as a viral infection, which part of the LN will enlarge?
Paracortex (contains endothelial venules for T and B cells to enter; houses T cells)
what structure drains lymph from the R side of the body above the diaphragm?
what does it drain into?
Right lymphatic duct.
Drains into junction of R internal jugular and R subclavian v
what structure drains lymph from everything except the R side of the body above the diaphragm?
what does it drain into?
Thoracic Duct.
Drains into Left Subclavian
what are the three main parts of a splenic sinusoid, and what is found at each place?
- Periarterial lymphatic sheath within white pulp: T cells
- Follicies within the white pulp: B cells (germinal centers)
- Marginal zone (btwn red pulp and white pulp): APCs and specialized B cells.
within a splenic sinusoid, where do APCs present their antigens?
in the marginal zone, between red pulp and white pulp
macrophages in the spleen remove what type of organisms?
encapsulated bacteria
2 reasons for splenic dysfunction?
how does splenic dysfunction lead to increased susceptability to encapsulated organisms?
splenectomy; sickle cell disease
Decreased IgM -> decreased complement activation -> decreased C3b opsonization -> increased susceptability to encapsulated organisms
what are the encapsulated bacteria that we worry about with asplenic patients?
SHiNE SKiS:
Strep pneumo
H influenza type B
Neisseria meningitidis (polysaccharide capsule: LOS)
E coli (K capsule)
Salmonella (Vi capsule)
Klebsiella (K capsule)
Group B Strep
what occurs in the Thymus?
from what embryonic structure does it derive?
T cell differentiation and maturation
From epithelium of 3rd pharyngeal pouches
(lymphocytes of mesenchymal origin)
Thymus: 2 parts? what cells are in each?
- Cortex: dense, holds immature T cells
- Medulla: pale, mature T cells & Hassall corpuscules containing epithelial reticular cells
T reg cells: what do they do?
what do they secrete?
what surface markers do they express? (4)
- help maintain specific immune tolerance by suppressing CD4 and CD8 T cell functions
- Secrete IL-10 and TGF-beta (anti-inflammatory cytokines)
- Surface markers: CD3, CD4, CD25 (alpha chain of the IL-2 receptor), & tsn factor FOXP3
What do activated Treg cells do?
Produce anti-inflammatory cytokines (such as IL-10 and TGF-beta)
what parts of antibodies recognize antigens? heavy chain or light chain?
where is the antigen-binding site?
The variable parts of both Light and Heavy chains recognize antigens. (outermost portion of each chain)
antigen binding site is between the two chains on each side.
what portion of antibodies fixes complement?
The Fc portion. binds both complement and macrophages.
what part of an antibody determines its idiotype?
the Fab portion.
contains antigen-binding site, determines idiotype.
only one antigenic specificity expressed per B cell.
What are the 4 C’s of the Fc portion of an antibody? what is the 5th thing that the Fc portion does?
- Constant region
- Carboxy terminal
- Complement binding
- Carbohydrate side chains
- Determines Isotype (IgM, IgD, etc)
How is antibody diversity generated? (4 ways)
- random recombination of VJ (light chain) or VJ/VDJ (heavy chain) genes
- random combination of heavy chains with light chains
- somatic hypermutation following antigen stimulation
- addition of nucleotides to DNA during recombination by terminal deoxynucleotidyl transferase
what are the 5 immunoglobulin isotypes
IgG, IgA, IgM, IgD, IgE
mature B lymphocytes express what on their surface?
how do we get cells that express the other immunoglobulin isotypes?
Express IgM and IgD.
they differentiate into plasma cells that secrete IgA, IgE, IgG in germinal centers (LNs) by isotype switching.
what mediates the isotype switching of mature B lymphocytes?
isotype switching = gene rearrangement
mediated by cytokines and CD40 ligand
IgG: functions?
main AB in the delayed response to an antigen.
fixes complement, crosses placenta (gives fetus passive immunity), opsonizes bacteria, neutralizes bacterial toxins and viruses.
IgA: functions?
prevents attachment of bacteria and viruses to mucus membranes. does not fix complement.
crosses epithelial cells by transcytosis. released into secretions (tears, saliva, mucus, early breast milk/colostrum).
IgA: what form is it present in in circulation? in secretions?
Circulation - Monomer
secretions - dimer
IgM: functions?
produced in the immediate response to an antigen. Fixes complement
does not cross placenta
antigen rceptor on the surface of B cells (along with IgD).
IgM: what forms is it present in?
on B cell: monomer
in secretions: pentamer. shape of pentamer allows it to trap free antigens out of tissue while humoral response evolves (remember IgM = part of immediate response to antigen)
IgD: function? located where?
unclear function
found on the surface of many B cells and in serum
IgE: function?
- Binds mast cells and basophils; cross links when exposed to allergen
- mediates Type I/immediate hypersensitivity reaction thru release of inflammatory mediators such as histamine.
- Mediates immunity to worms by activating eosinophils.
which immunoglobin isotype is most abundant in serum? least?
most abundant: IgG
lowest concentration: IgE
what are thymus-independent antigens?
- antigens lacking a peptide component. cannot be presented by MHC to T cells.
- weakly- or non-immunogenic; vaccines often require boosters (ex pneumococcal polysaccharide vaccine)
what are thymus-dependent antigens?
- antigen containing a protein component.
- class switching and immunologic memory occur as a result of direct contact of B cells with Th cells (remember the CD40-CD40L interaction)
what are acute phase reactants? where are they produced? what induces them?
- factors whose serum concentrations change significantly in response to inflammation
- produced by the liver in both acute and chronic inflammatory states.
- Induced by IL-6, IL-1, TNF-alpha, IFN-gamma
what acute phase reactants are upregulated in response to inflammation?
Serum amyloid A
CRP
Ferritin
Fibrinogen
Hepcidin
Each of these acute phase reactants is upregulated in response to inflammation: what does each do?
Serum amyloid A
CRP
Ferritin
Fibrinogen
Hepcidin
Serum amyloid A: function not given. (prolonged elevation can lead to amyloidosis)
CRP: Opsonin; fixes complement, facilitates phagocytosis. Measured clinically as a sign of 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 -> anemia of chronic disease
what are the 2 acute phase reactants that are downregulated with inflammation? what does each do?
- Albumin: reduction of albumin conserves amino acids for the reactants that are upregulated with inflammation
- Transferrin: internalized by macrophages to sequester iron
Complement: what is a general overview?
system of interacting plasma proteins that play a role in innate immunity and inflammation.
MAC defends against gram-neg bacteria.
Complement system: three methods of activation?
- Classic pathway: IgG or IgM mediated (GM makes Classic cars)
- Alternative pathway: microbe surface molecules
- Lectin pathway: mannose or other sugars on microbe surface
(See FA’14 p204 for extensive diagram)
Describe the functions of each of these parts of the complement cascade:
C3b
C3a, C4a, C5a
C5a
C5b-C9
C3b: Opsonization (C3b binds bacteria)
C3a, C4a, C5a: anaphylaxis (aaaa)
C5a: neutrophil chemotaxis
C5b-C9: cytolysis by Membrane Attack Complex (Big MAC attack)
describe this complement disorder: C1 esterase inhibitor deficiency.
causes hereditary angioedema.
ACE inhibitors are contraindicated
(C1 is part of both the Lectin and Classic activation pathways)
describe this complement disorder: C3 deficiency.
Increases risk of severe, recurrent pyogenic sinus and resp tract infections.
Increases susceptibility to Type III hypersens reactions.
describe this complement disorder: C5-C9 deficiencies.
Increased susceptibility to recurrent Neisseria bacteremia
(recall C5-C9 –> MAC/membrane attack complex which causes cytolysis)
describe this complement disorder: DAF (GPI anchored enzyme) deficiency.
Causes complement-mediated lysis of RBCs and paroxymal nocturnal hemoglobinuria
Macrophages secrete 5 impt cytokines. what are they?
IL-1, IL-6, IL-8, IL-12, TNF-alpha
briefly, what are the functions of IL-1 through IL-6?
(hints: generally they stimulate things. also there is an acronym)
HOT T-bone stEAK:
IL-1: Hot (fever)
IL-2: stimulates T cells
IL-3: stimulates bone marrow
IL-4: stimulates IgE production
IL-5: stimulates IgA production
IL-6: stimulates aKute-phase protein production