Question

The antibody response to thymus-independent antigens does NOT require T cell help because _______

a. some highly repetitive epitopes cause extensive crosslinking of the BCRs and their co-receptors, and can activate mature naive B cells.
b. the B cell uses ADCC to become activated.
c. C3b covers the B-cell surface entirely, eliminating the need for T-cell help.
d. somatic hypermutation and isotype switching typically happens in the TCRs.

Answer 1

The antibody response to thymus-independent antigens does not require T cell help because repetitive epitopes on the antigen lead to the crosslinking of BCRs, which activates B cells without the need for T cell involvement. The correct choice is (a), highlighting the importance of BCR crosslinking in T cell-independent activation.

Step-by-step explanation:

The antibody response to thymus-independent antigens does not require T cell help because some highly repetitive epitopes cause extensive crosslinking of the BCRs and their co-receptors, which can activate mature naive B cells. This process is known as T cell-independent activation of B cells, and it typically occurs with antigens that have repetitive epitope units within their structure, such as polysaccharide capsules or lipopolysaccharide found on bacteria. These repetitive units allow for the cross-linkage of multiple BCRs, providing the signal necessary for B cell activation without the need for T cell involvement.

The correct answer to the student's question is (a), as T-independent antigens enable the cross-linkage of BCRs on the B cell surface due to their repeated nature, thereby activating the B cell in the absence of help from T cell cytokines. This crosslinking is sufficient to activate B cells, leading to the production of IgM antibodies by plasma cells.