Immunofluorescence studies on the expression of VHa allotypes by pre‐B and B cells of homozygous and heterozygous rabbits

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Abstract
Fluorochrome‐conjugated antibodies specific for Cμ determinants and VHa allotypes were used to examine pre‐B cells and B lymphocytes for expression of these markers. The majority of μ+ bone marrow pre‐B cells were shown to express a allotypic determinants in conjunction with Cμ. Both pre‐B and B cells from a2a3 heterozygous rabbits showed allelic exclusion of these allotypes. Pre‐B cells expressing the a2 or a3 specificities appeared to be generated in approximately equal numbers in heterozygotes, while B lymphocytes expressing a3 appeared to undergo preferential clonal expansion very early in development. It was also observed that rabbit bone marrow and blood contained a population of myeloid cells which, in a2a3 heterozygotes, stained for both a2 and a3 determinants. The frequencies of this cell type, which exhibited bright immunofluorescence staining for a allotypes, could not be reduced by prolonged incubation at 37°C but were readily reduced after cell suspensions were treated with low pH buffer. It is concluded that these myeloid cells bear high avidity Fc receptors for serum immunoglobulin and may be the culprits in studies which have found production of two a or b allotypes by individual B lymphocytes.