Adaptive Immune Response

Free Response

Explain the difference between an epitope and an antigen.


An antigen is a molecule that reacts with some component of the immune response (antibody, B cell receptor, T cell receptor). An epitope is the region on the antigen through which binding with the immune component actually occurs.

What is a naïve B or T cell?


A naïve T or B cell is one that has not been activated by binding to the appropriate epitope. Naïve T and B cells cannot produce responses.

How does the TH1 response differ from the TH2 response?


The TH1 response involves the secretion of cytokines to stimulate macrophages and CTLs and improve their destruction of intracellular pathogens and tumor cells. It is associated with inflammation. The TH2 response is involved in the stimulation of B cells into plasma cells that synthesize and secrete antibodies.

In mammalian adaptive immune systems, T cell receptors are extraordinarily diverse. What function of the immune system results from this diversity, and how is this diversity achieved?


The diversity of TCRs allows the immune system to have millions of different T cells, and thereby to be specific in distinguishing antigens. This diversity arises from mutation and recombination in the genes that encode the variable regions of TCRs.

How do B and T cells differ with respect to antigens that they bind?


T cells bind antigens that have been digested and embedded in MHC molecules by APCs. In contrast, B cells function themselves as APCs to bind intact, unprocessed antigens.

Why is the immune response after reinfection much faster than the adaptive immune response after the initial infection?


Upon reinfection, the memory cells will immediately differentiate into plasma cells and CTLs without input from APCs or TH cells. In contrast, the adaptive immune response to the initial infection requires time for naïve B and T cells with the appropriate antigen specificities to be identified and activated.