Figure 1. Characteristic features of the antibody (Ab) (B cell) response. (a) Activation of B cells by T-dependent antigen. (b) Activation of B cells by T-independent antigen. (c) Comparison of primary and secondary antibody (B cell) response. (d) Clonal selection and expansion of the B-cell (antibody) response. Antigen (Ag) stimulates three antigen-specific B-cell clones out of the preimmune B-cell repertoire. The blue clone (–+) has low affinity for antigen, but high adaptability; the pink clone (+–) has high affinity and low adaptability; the green clone (++) has high affinity and high adaptability. During the primary response (excess of Ag) these clones expand equally. However, during the development of the antibody response, Ag may become a limiting factor and somatic mutations (indicated by red dots) begin to accumulate in the antibody's V regions and stringent selection occurs; the pink and green clones expand and accumulate. As this process continues even further, the green clone (i.e. the clone displaying both high affinity and high adaptability) will dominate. Ig, immunoglobulin; TCR, T-cell receptor; T_H, T-helper cell.

Figure 2. Schematic illustration of the affinity maturation process. Ag, antigen; FDC, follicular dendritic cell; GC, germinal centre; T_H, T-helper cell.

Figure 3. Schematic illustration of class switching. IFN, interferon; Ig, immunoglobulin; IL, interleukin.