1)Binding of microbial molecules by toll-like receptors (TLRs) on a phagocytic c
ID: 3508541 • Letter: 1
Question
1)Binding of microbial molecules by toll-like receptors (TLRs) on a phagocytic cell should lead to:
A. Activation of the phagocyte
B. Death of phagocyte by apoptosis
C. Production of IL-2
D. Induction of CD3 expression on phagocyte membrane
2)Antigen binding by antibody molecules is primarily a function of what?
A. Hypervariability regions of VH
B. Hypervariability region of VL
C. Hypervariability region of Fc and Fab
D. All of the above
3) _____ B and T cells are mature lymphocytes that have not been stimulated by antigen. When they encounter antigen, they differentiate into ______ lymphocytes that have functions in protective immune responses.
A. Effector, naive
B. Naive, effector
C. Naive, CTLs
D. Effector, CTLs
Explanation / Answer
1. Toll like receptors are membrane spanning proteins having a major role in innate immunity. These are noncatalytic receptors found on phagocytic cells such as macrophages and dendritic cells. Binding of microbes on toll like receptors of phagocytic cells trigger signal transdution pathway to recruit the protein kinases activating the phagocytes. The phagocytosis of bacterial pathogen is initiated and antigen is digested. Binding of viral antigens inhibit the protein synthesis in such cells and the infected cells are subjected to apoptosis or programmed cell death. Option A is correct.
2. The antigen binding is the major function of Fab region in IgG molecule. The close association of variable region(V), heavy chain (H) and light chain (L) produce a cavity for fitting of antigen and Fc region carries out other interactions regulating the processing of antigen. Thus the option D is correct.
3. The naive B and T cells are mature cells but does not have the exposure to the antigen. The B and T cells encountered with antigen are called effector cells because they are activated by the antigen and are ready to process the antigen and eliminate from the host body. Thus, the option B is correct.
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