Immunology Flashcards
Immunoglobulin heavy chains: Domains.
One variable domain and 3-4 constant domains.
Paratope: Definition.
The part of the immunoglobulin molecular that binds the antigen.
Location of genes for immunoglobulin light chains and heavy chains.
Light chains: Chromosomes 2 (κ) and 22 (λ).
Heavy chains: Chromosome 14.
First step in rearrangement of immunoglobulin genes in B cells.
Rearrangement of genes for variable regions: V and J regions of light chains and V, D, and J regions of heavy chains.
Second step in rearrangement of immunoglobulin genes in B cells.
The rearranged sequences of the variable regions are joined to a gene sequence of a constant region of a light chain or heavy chain. The initial heavy-chain constant region is always μ.
Immunoglobulins on mature B cells.
IgM and IgD.
What happens when a helper T cell stimulates a mature B cell?
The B cell proliferates, and each progeny joins its prefabricated variable-gene sequences to a gene for a different heavy chain. This is isotope switching.
Idiotope: Definition.
The part of the (variable region of the) immunoglobulin molecule that can function as an epitope.
Which classes of immunoglobulin have subclasses?
IgG: 4 subclasses.
IgA: 2 subclasses.
Which classes of immunoglobulin can activate complement?
IgG1, IgG3, IgM: Classic pathway.
IgA: Alternate pathway.
Which class of immunoglobulin is the least abundant?
IgE.
Genes for the T-cell receptor:
A. Number.
B. Location.
A. Four genes: α, β, γ, δ.
B. Chromosome 7.
Types of T-cell receptors.
αβ: 95% of T lymphocytes.
γδ: Mostly in mucous membranes and skin.
NK cells:
A. Percentage of circulating lymphocytes.
B. TCR and immunoglobulin.
A. About 10%.
B. Not expressed; genes remain in germline state.
NK cells: Surface markers.
Positive: CD16, CD56, CD57.
Negative: CD3.
NK cells: Purpose of CD16.
As the FcγR, it binds opsonized cells, mediating antigen-dependent cytotoxicity.
NK cells: Functions.
Combating virus-infected cells and tumor cells.
Secreting IFNγ.
Antigen-presenting cells: Immunity-mediating antigens expressed on their surfaces.
All: MHC class II, CD68, lysozyme.
All but monocytes and macrophages: S100, CD1a.
Antigen-presenting cells: Secretion.
Interleukin 1.
Chemokine that attracts neutrophils.
Interleukin 8 (among others).
How basophils and mast cells come to release the contents of their granules.
They use their Fcε to bind IgE, the cross-linking of which promotes degranulation.
Cytokines that stimulate eosinophils.
IL-4 stimulates production of IgE.
IL-5 attracts eosinophils.
Both interleukins are secreted by Th2 cells.
Charcot-Leyden crystals:
A. Origin.
B. Function.
A. Degranulation of eosinophils.
B. They have lysophospholipase activity.
Complement: Final common pathway.
Formation of C5b6789, the membrane-attack complex.
Complement: Activators of the classic pathway.
Antigen-antibody complexes of IgG or IgM.
Complement: Classic pathway to the formation of the C3 convertase.
The Fc portion of the immunoglobulin molecule binds to C1q. Activated C1 catalyzes the formation of C4b2a.
Complement: Classic pathway from the formation of the C3 convertase.
C4b2a converts C3 to C3a and C3b. The latter joins the complex to make C4b2a3b, the C5 convertase, which yields C5b.
Complement: Alternative pathway to the formation of the C3 convertase.
Constitutively produced C3b binds to Bb (produced by the action of factor D on factor B). This C3bBb is the C5 convertase.
Complement: Alternative pathway from the formation of the C3 convertase.
C3Bb acts on C3 to make more C3b. The resulting C3Bb3b is the C5 convertase.
Complement: Regulators of the alternative pathway.
Factor I inactivates C3 unless the latter is bound, for example, to a bacterial cell wall.
Properdin stabilizes the C3 and C5 complexes.
Complement: Activators of the mannan-binding-lectin pathway.
Carbohydrates of non-mammalian cells, specifically those of Salmonella, Listeria, Neisseria, Candida, Cryptococcus.
Complement: Mannan-binding-lectin (MBL) pathway to the association with MASPs.
Binding of mannose-binding lectin binds to the microbial surface allows MBL to associate with MASPs (MBL-associated serine proteases).
Complement: Mannose-binding-lectin pathway from the association with MASPs.
MASP-2 cleaves C4 and C2, thus bypassing C1 and obviating the need for antigen-antibody complexes. C4b2a is the C3 convertase.
Complement: The anaphylotoxins.
C3a and C5a, which promote the release of histamine from basophils.
Complement: Rôle of decay-accelerating factor.
Accelerates the decay of the C3 and C5 convertases.
Complement: Activators of the alternative pathway.
Bacterial cell walls, venoms, endotoxins, complexed IgA.
HLA class I molecules: Components.
Heavy chain: Three α domains.
Light chain: β₂-microglobulin.
HLA class I molecules: Distribution on body cells.
Found on most nucleated cells.
HLA class I molecules: Function.
Mediation of the function of CD8-positive T cells, which kill cells that express foreign antigen in conjunction with their class I molecules.
HLA class II molecules: Components.
An α chain and a β chain, each of which has
Two domains similar to the immunoglobulin light chains.
A transmembrane domain.
HLA class II molecules: Distribution on body cells.
Found on B cells, antigen-presenting cells, and activated T cells.
Primary immunodeficiencies: Who is mainly affected?
Males.
Defects of immunoglobulins or of B cells: Clinical manifestations.
Recurrent bacterial infections of the respiratory tract, ultimately leading to bronchiectasis.
Recalcitrant intestinal infections such as with Giardia intestinalis.
Defects in T cells: Clinical manifestations.
Viral and fungal infections, e.g. mucocutaneous candidiasis.
Defects of phagocyte: Clinical manifestations.
Infections by staphylococci and other catalase-positive organisms.
Defects in terminal components of complement: Clinical manifestations.
Severe infections by encapsulated organisms such as N. meningitidis and S. pneumoniae.
Primary immunodeficiencies: Possible findings on physical examination.
Large lymph nodes: Common-variable immunodeficiency, chronic granulomatous disease.
Small lymph nodes: Other B-cell deficiencies.
Petechiae, easy bruising: Wiskott-Aldrich syndrome.
How injection of antigens can be used to determine the type of immunological defect.
Impaired response to protein antigens (tetanus toxoid, diphtheria toxoid): Defect in T cells, B cells, or both.
Impaired response to carbohydrate antigens (pneumococcal or meningococcal vaccine): Defect in B cells.
RAST:
A. Meaning.
B. Principle.
A. Radioallergosorbent test.
B. The amount of IgE production elicited by an antigen is measured.
Specific tests of T-cell function.
Flow cytometry.
Tests of delayed-type hypersensitivity.
Proliferation assays.
Proliferation assays for T cells:
A. Agents.
B. What gets measured?
A. Concanavalin A, phytohemagglutinin.
B. The uptake of tritiated thymidine.
Tests of NK-cell function.
Chromium-release assays.
Colorimetric detection of granzyme B.
Nitroblue tetrazolium test: Principle.
A neutrophil capable of generating a normal oxidative burst will reduce yellow NBT to purple-blue formazan.
Nitroblue tetrazolium test: Interpretation.
~100% of neutrophils are F+: Normal.
<10%: Chronic granulomatous disease.
Use of flow cytometry to test for oxidative burst in neutrophils.
Oxidation of dihydrorhodamine 123 produces fluorescence that can be measured.
CH50 test:
A. Purpose.
B. Method.
C. Reported value.
A. To assess function of the classic pathway.
B. One determines the dilution of the patient’s serum that lyses 50% of immunoglobulin-coated sheep erythrocytes.
C. The reciprocal of the dilution.
Causes of deceased C3.
Primary deficiency of C3.
Activation of the alternative pathway.
Complement components measured in assessing the function of the classic pathway.
C4, C1q.
Uses of the complement-dependent-cytotoxicity assay (3).
Detecting HLA antigens or antibodies to them.
Performing HLA crossmatches.
Mixed lymphocyte culture: Purpose.
To detect differences in HLA class II antigens between a potential donor and a recipient.
Cross-reactive antigen group: Definition.
Group of HLA alleles for which there is serologic cross-reactivity.
Public antigen:
A. Definition.
B. Example.
A. A sequence of amino acids shared among many different HLA antigens.
B. HLA-Bw4, HLA-Bw6.
Public antigens: Significance.
In someone lacking a public antigen, sensitization can appear as many different HLA antibodies. This can complicate platelet transfusions and organ transplants.
Advantage of PCR in HLA typing.
Distinguishes among HLA types more precisely than does serology.
Panel-reactive-antibody tests:
A. Purpose.
B. Principle.
A. To help find a donor for a patient needing a transplant.
B. One determines the proportion of the donor population against which the patient’s HLA antibodies will react.
Panel-reactive-antibody tests: Reporting of results.
A PRA of 80% means that the patient has about a 20% chance of finding a compatible organ from an unrelated donor.
HLA matching for transplantation: Most important loci.
HLA-A, HLA-B, HLA-DR.
How to prevent hyperacute rejection.
Use the complement-dependent-cytotoxicity (CDC) assay to detect preformed antibodies against HLA antigens in the potential donor.
Advantages of flow cytometry in the crossmatching of transplants.
More sensitive than the CDC assay.
Detects lower titers of complement-dependent and complement-independent antibodies to the donor graft.
Correlation of Luminex technology with other techniques for crossmatching of transplants.
MFI (mean fluorescence intensity) . . .
> 5000: Correlates with incompatibility on flow cytometry of T and B cells.
> 10,000: Correlates with a positive CDC assay and the likelihood of hyperacute rejection.
Required compatibilities for transplantation of
A. Kidney.
B. Liver.
C. Heart.
D. Lung.
A. ABO, HLA, crossmatch.
B,C,D. Only ABO compatibility is required.
Required HLA compatibility for transplantation of allogeneic progenitor cells.
HLA-A, -B, -C, -DRB1.
Hyperacute rejection:
A. Onset.
B. Location of inciting antigens.
A. Within hours.
B. On the endothelium of the graft.
Hyperacute rejection: Histology.
Fibrin thrombi, platelet thrombi, necrosis, all due to complement-mediated vascular injury
Acute cellular rejection:
A. Onset.
B. Mechanism.
A. Evolves over days to weeks.
B. The recipient’s T cells recognize the donor’s HLA antigens as foreign and mount a powerful cytotoxic response.
Acute cellular rejection: Histology.
Lymphocytic infiltration of epithelium (tubulitis) and endothelium, along with interstitial edema.
Acute humoral rejection:
A. Onset.
B. Mechanism.
A. Within days or weeks.
B. Antibodies against the endothelium of the graft.
Acute humoral rejection: Histology (2).
Fibrinoid necrosis and neutrophilic infiltration of vessel walls, resulting in infarction.
- or -
Subendothelial intimal thickening with more protracted ischemia of the graft.
Acute humoral rejection: Patients at high risk.
Those who have been previously immunized against HLA antigens, due to pregnancy or transfusion.
Acute humoral rejection: Immunohistochemistry.
Demonstrates deposition of C4d in vessel walls.
Chronic rejection:
A. Onset.
B. Mechanism.
A. Develops over months or years.
B. Mediated by both lymphocytes and antibodies.
Chronic rejection: Histology.
Interstitial fibrosis, arteriolosclerosis, deposits of complement in peritubular vessels.
Graft-versus-host disease: Required conditions.
Immunocompetent T cells from the donor.
Immunosuppressed recipient.
Antigenic differences between donor and recipient.
Acute GVHD:
A. Onset.
B. Affected organs.
A. Within 100 days after transplant; usually within 30 days.
B. Skin, intestinal tract, hepatobiliary tract.
Acute GVHD: Effect on skin.
Red, itchy rash.
Histology: Apoptosis similar to that found in erythema multiforme.
Acute GVHD: Effect on intestinal tract.
Diarrhea.
Histology: Ectatic crypts with attenuated enterocytes, crypt abscesses, and apoptosis.
Acute GVHD: Effect on hepatobiliary tract.
Jaundice.
Histology: Mononuclear infiltrate in portal areas, with endothelialitis, ductitis, ductopenia.
Chronic GVHD:
A. Onset.
B. Affected organs.
A. >100 days after transplant.
B. Skin, intestinal tract, hepatobiliary tract; mucosa of mouth, vagina, eye, respiratory tract.
Chronic GVHD: Effect on
A. Skin.
B. Esophagus.
C. Eyes.
A. Extensive sclerosis.
B. Strictures.
C. Scarring lesions.
Bruton’s agammaglobulinemia:
A. Onset.
B. Infections.
C. Other complications.
A. Around 6 months of age.
B. Bacterial, enteroviral; viral hepatitis.
C. Lymphoid neoplasms, autoimmune diseases.
Bruton’s agammaglobulinemia: Laboratory findings.
Marked reduction in serum immunoglobulins.
Lack of CD19-positive B cells.
Bruton’s agammaglobulinemia: Physical examination.
Rudimentary lymph nodes and tonsils.
Bruton’s agammaglobulinemia: Gene and its location.
BTK on the X chromosome.
Common-variable immunodeficiency:
A. Onset.
B. Infections.
C. Other complications.
A. Second or third decade.
B. Recurrent infections of upper and lower respiratory tract; giardiasis.
C. Bronchiectasis, intestinal bacterial overgrowth.
Common-variable immunodeficiency: Laboratory findings.
Decreased serum immunoglobulins.
Variable T-cell deficiency.
Common-variable immunodeficiency: Histology.
Lack of plasma cells.
Reactive follicular hyperplasia; hyperplastic germinal centers.
Common-variable immunodeficiency: Underlying defect.
Excess of Th1 cells -> overproduction of IL-12 -> suppression of Th2 cells -> decreased stimulation of B cells to produce antibody.
Selective IgA deficiency:
A. Incidence.
B. Infections.
C. Other complications.
A. 1 in 700.
B. Respiratory and gastrointestinal; many patients have none.
C. Autoimmune disease; anaphylactic transfusion reaction.