Analysis of B cell selection in the germinal center reaction during a T-dependent antibody response at a single cell level

Abstract

The quasimonoclonal mouse is useful to examine B cell selection during T-dependent antibody (Ab) responses because of its limited B cell populations mainly expressing the knockin 17.2.25 V H-encoded H chain (V HT) paired with the λ1 or λ2 L chain. It has been reported that both two V HT/λ1 and V HT/λ2 B cell populations responded to a T-dependent antigen conjugated with a hapten p-nitrophenylacetyl ( pNP), but only V HT/λ2 B cells differentiated to secrete high affinity anti- pNP IgG Abs by acquiring a critical mutation (T313A) in the V HT. The V HT/λ2 B cells may be more potent in migrating to the germinal centers (GCs) due to about 50-fold higher affinity for pNP than V HT/λ1 B cells. Here, to uncover how V HT/λ2 B cells were preferentially recruited for affinity maturation during the anti- pNP Ab response, we examined the L chain usage and mutation frequency of V HT + GC B cells at a single cell level. V HT/λ2 B cells bearing the unmutated V HT gene were found in the GCs more frequently than V HT/λ1 and mutated V HT/λ2 counterparts in an early phase of the Ab response. In the course of the GC reaction, the number of V HT/λ2 B cells that mutated their V HT genes preferentially expanded, and finally V HT/λ2 B cells bearing the T313A mutation occupied V HT + GC B cell population. Thus, it is suggested that B cells with a higher affinity were selected not only for entry to the GCs but also in the affinity maturation process during a T-dependent Ab response.