MLT GlobeImmunology & Serology: Immune system principles – page 11
257 Immunology & Serology MCQs on Immune system principles with answers and explanations.
Peptides from viral proteins made in the cytosol are carried into the endoplasmic reticulum for loading onto MHC class I by:
Proteasome-generated peptides are pumped into the ER by TAP1/TAP2 and loaded onto class I molecules. The invariant chain and HLA-DM belong to the class II pathway.
A complete MHC class I molecule on the cell surface consists of:
Class I is an MHC-encoded α chain non-covalently bound to β2-microglobulin, which is encoded on chromosome 15. The α/β pair of MHC-encoded chains describes class II.
The HLA class III region of the MHC encodes:
Class III genes lie between class I and II and include C2, C4, factor B and TNF. β2-microglobulin is encoded outside the MHC, on chromosome 15.
A patient needs a stem cell donor. Assuming no recombination, what is the chance that one full sibling is HLA-identical to the patient?
HLA genes are inherited as two parental haplotypes; a sibling has a 1 in 4 chance of receiving the same two haplotypes. 50% is the chance of sharing exactly one haplotype.
A patient with suspected coeliac disease has HLA typing. Absence of which alleles makes coeliac disease very unlikely?
Nearly all coeliac patients carry HLA-DQ2 or DQ8, so a negative result has a very high negative predictive value. HLA-B27 relates to spondyloarthritis.
Mycobacterial lipid and glycolipid antigens are presented to T cells by which molecules?
CD1 molecules are MHC-like proteins that present lipid antigens to certain T cells, including NKT cells. Classical MHC molecules present peptides.
In normal human serum, the approximate ratio of kappa-bearing to lambda-bearing immunoglobulin molecules is:
About two-thirds of human immunoglobulins carry kappa and one-third lambda light chains. A marked change in this ratio suggests a clonal B-cell population.
IgG has a serum half-life of about 3 weeks, much longer than other classes. This is mainly because:
FcRn binds IgG in endosomes and recycles it back to the circulation instead of letting it be degraded. IgG has no J chain or secretory component.
Which of these immunoglobulin classes has the shortest half-life in serum?
Free serum IgE has a half-life of only about 2 days, although IgE bound to mast cells lasts much longer. IgG lasts about 21–23 days.
Digestion of IgG with pepsin produces:
Pepsin cuts below the hinge disulfide bonds, leaving a bivalent F(ab')2 that can still agglutinate or precipitate, while Fc is degraded. Two Fab plus Fc is the papain product.
The secretory component attached to secretory IgA is derived from:
Epithelial cells bind dimeric IgA with the polymeric Ig receptor and transport it across the cell; part of the receptor stays attached as secretory component. The J chain is made by plasma cells.
Which immunoglobulin class is produced in the largest total amount each day, mostly in mucosal tissues?
Mucosal plasma cells secrete several grams of IgA daily, more than all other classes combined, but much is lost into secretions. IgG is highest in serum only because of its long half-life.
A flow cytometry report shows WBC 5.0 × 10⁹/L, lymphocytes 20%, and CD4+ T cells 25% of lymphocytes. The absolute CD4 count is:
5.0 × 10⁹/L × 0.20 = 1.0 × 10⁹/L lymphocytes; × 0.25 = 0.25 × 10⁹/L, which is 250 cells/µL. 1000 cells/µL is the absolute lymphocyte count.
What is the theoretical antigen-binding valence of a pentameric IgM molecule?
Each of the five monomers has two antigen-binding sites, giving a valence of 10. In practice, steric hindrance often allows only about 5 sites to bind large antigens.
Serum for classical complement studies was accidentally collected in an EDTA tube. Classical pathway activity will be absent mainly because EDTA:
C1q, C1r and C1s need Ca²⁺ to stay assembled; the alternative pathway needs Mg²⁺, which EDTA also removes. Serum, not EDTA plasma, is the specimen for functional complement tests.
In the lectin pathway, mannose-binding lectin binds microbial carbohydrates and activates which enzymes to cleave C4 and C2?
MBL-associated serine proteases (MASPs) act like C1r/C1s and cleave C4 and C2 without antibody. Factor B and factor D belong to the alternative pathway.
The role of properdin in the alternative complement pathway is to:
Properdin (factor P) binds C3bBb and extends its half-life several-fold, amplifying C3 cleavage. Cleavage of factor B is done by factor D.
Cleavage of cell-bound C3b to inactive iC3b is carried out by which plasma protease, working with cofactors such as factor H?
Factor I cleaves C3b and C4b only in the presence of a cofactor (factor H, C4-binding protein, CR1 or MCP). Factor D cleaves factor B.
Inherited deficiency of early classical pathway components (C1q, C2 or C4) is most strongly associated with:
Early classical components help clear immune complexes and apoptotic cells; without them, lupus-like autoimmunity develops (especially with C1q deficiency). Neisseria infections relate to terminal component deficiency.
Complement receptor 1 (CR1, CD35) on human red cells mainly helps to:
C3b-coated immune complexes bind CR1 on red cells and are stripped off by macrophages in the liver and spleen. CR1 also acts as a cofactor for factor I.