ANTIGEN‐DEPENDENT B‐LYMPHOCYTE DIFFERENTIATION

Summary Preparative, free‐buffer film electrophoretic separation of mouse lymphocytes revealed B cell heterogeneity. The typical B cell was of low electrophoretic mobility. However, both very low mobility recirculating B cells and high mobility larger‐sized B cells were separated in spleen. In imprimed mice the AFC‐progenitor activity† for an IgM response to NIP‐POL antigen was absent from the slowest migrating B cells and was enriched amongst the “atypical” fast migrating elements. In contrast, the progenitor activity for a memory IgG response in NIP‐primed mice was absent from the fast migrating regions and was enriched amongst the slowest migrating B cells. The progenitor activity for IgM responses in NIP‐primed mice was intermediate between these situations. The B cell AFC‐progenitors for DNP‐POL and SRC antigens in the spleens of unprimed mice displayed many of the characteristics of the progenitors for an anti‐NIP response, and much of the activity was amongst the fast migrating, “atypical” B cells. The unprimed IgM and IgG response to SRC, however, was also found in slow migrating regions characteristic of the “memory” response to NIP, suggesting that a naturally pre‐primed state existed. The electrophoretic characteristics of AFC at the peak of a response differed from those of their progenitor cells. With all antigens, and with both pre‐primed and normal animals. AFC showed a broad distribution with a peak in the medium mobility region. Background AFC for SRC showed the same characteristics as those at the peak of a response. In contrast, the few background AFC for the NIP‐determinant were of low mobility.