A common strategy by which microbes survive their host's immune responses involves changing the structures of the molecules they produce so that they are no longer recognized by the host's immune system

Question

This strategy, called antigenic variation, is most likely to allow evasion of which type of immune recognition?

A. Toll-like receptor-dependent recognition of microbes by cells of the innate immune system
B. Mannose receptor-dependent recognition of microbes by cells of the innate immune system
C. Antibody recognition of microbial cell surface molecules
D. Natural killer cell inhibitory receptor recognition of class I major histocompatibility complex (MHC) molecules on infected cells
E. T cell receptor recognition of microbial cell wall lipid antigens

Answer 1

ANS: C. Antigenic variation allows microbes to evade adaptive immune recognition, usually by antibodies, but also by T cells. Antigenic variation usually involves mutations or recombination events in microbial genes encoding cell surface proteins or encoding enzymes involved in synthesis of cell surface sugars. The result changes microbial surface antigens. This is an effective strategy, because many of the microbial antigenic structures that the adaptive immune system recognizes, are not essential for survival or virulence of the microbe. In contrast, most structures recognized by receptors of the innate immune system (e.g., Toll-like receptor and scavenger receptor ligands) are essential for microbial survival and, as such, cannot undergo antigenic variation. Although some viruses may block class I major histocompatibility complex (MHC) expression by infected cells, this renders the cells more susceptible to natural killer cell-mediated killing and is not antigenic variation by the virus. Only a small subset of T cells recognizes lipid antigens, usually in association with CD1 molecules. There is no evidence for antigenic variation of the lipid antigens recognized by these T cells.