B cell antibody responses are classified by their dependence on helper T cell assistance: T-dependent antigens require antigen presentation by dendritic cells to naive T helper cells, which then interact with B cells (which themselves act as antigen-presenting cells) via CD40 ligand–CD40 binding and cytokine signaling to induce class switching to IgG, IgA, or IgE. T-independent antigens, typically possessing repeating structural elements that extensively cross-link the B cell receptor, activate B cell proliferation and differentiation without T cell help, but in the absence of CD40 ligand–CD40 interaction, class switching does not occur and only IgM (with minimal IgG) is secreted. This distinction illustrates a core organizing principle of adaptive humoral immunology: T cell costimulation is the mechanistic requirement for immunoglobulin class switch recombination.
B cell antibody responses are classified by their dependence on helper T cell assistance: T-dependent antigens require antigen presentation by dendritic cells to naive T helper cells, which then inte…