Analysis of antigen-stimulated B cell migration into germinal centers during the early stage of a T-dependent immune response

The quasimonoclonal (QM) mouse provides a model to analyze B cell selection because major B cell antigen receptors (BCR) are composed of the knockin VHDJH 17.2.25 (VHT) encoded H chain and the λ1 or λ2 L chain, thereby being specific for (4-hydoxy-3-nitrophenyl)acetyl (NP). We have reported that during a T-dependent antibody (Ab) response for a low-affinity NP analog p-nitrophenylacetyl (pNP), although VHT/λ1 and VHT/λ2 IgM were equally produced, VHT/λ2 IgG almost exclusively underwent affinity maturation toward pNP. The initial affinity of VHT/λ2 B cells for pNP was approximately 50–100-fold higher than that of VHT/λ1 B cells, suggesting a role of BCR affinity in recruiting B cells to affinity maturation processes. Here, we investigated whether the intensity of BCR signals could contribute to the selection of VHT/λ2 B cells for affinity maturation. VHT/λ2 B cells were more responsive to pNP than VHT/λ1 B cells in vitro. When CFSE-labeled QM B cells were transferred into the wild type mice where T cells had been primed with chicken γ-globulin (CGG), QM B cells challenged by pNP-conjugated CGG could be observed to get activated and migrate to GCs in the early phase of the T-dependent response to pNP–CGG. Adoptive transfer of sorted populations revealed that the VHT/λ2 B cell population was more potent in migration into GCs than the VHT/λ1 counterpart. Thus, it is suggested that the higher BCR affinity of VHT/λ2 B cells may be an initial cue for their recruitment to GCs during a T-dependent Ab response.