The Roles of γ1 Heavy Chain Membrane Expression and Cytoplasmic Tail in IgG1 Responses

In antibody responses, B cells switch from the expression of immunoglobulin (Ig) mu and delta heavy (H) chains to that of other Ig classes (alpha, gamma, or epsilon), each with a distinct effector function. Membrane-bound forms of alpha, gamma, and epsilon, but not mu and delta, have highly conserved cytoplasmic tails. Mutant mice unable to express membrane gamma1 H chains or producing tailless gamma1 H chains failed to generate efficient IgG1 responses and IgG1 memory. H chain membrane expression after class switching is thus required for these functions, and class switching equips the B cell antigen receptor with a regulatory cytoplasmic tail that naïve B cells lack.