Selection of antigen-specific, idiotype-positive B Cells in transgenic mice expressing a rearranged M167-μ heavy chain gene

Abstract

Flow cytometric analysis of antigen-specific, idiotype-positive (id+), B cell development in transgenic mice expressing a rearranged M167-μ gene shows that large numbers of phosphocholine (PC)-specific, M167-id+ B cells develop in the spleen and bone marrow of these mice. Random rearrangement of endogenous Vκ genes, in the absence of a subsequent receptor-driven selection, should give rise to equal numbers of T15- and M167-id+ B cells. The observed 100-500-fold amplification of M167-id+ B cells expressing an endogenous encoded Vκ24Jκ5 light chain in association with the M167 VH1-id transgene product appears to be an antigen driven, receptor-mediated process, since no amplification of non-PC-binding M167 VH1/Vκ22, T15-id+ B cells occurs in these μ-only transgenic mice. The selection and amplification of antigen-specific, M167-id+ B cells requires surface expression of the μ transgene product; thus, no enhancement of M167-id+ B cells occurs in the M167 μΔmem-transgenic mice, which cannot insert the μ transgene product into the B cell membrane. Surprisingly, no selection of PC-specific B cells occurs in M167-K-transgenic mice although large numbers of B cells expressing a crossreactive M167-id are present in the spleen and bone marrow of these mice. The failure to develop detectable numbers of M167-id+, PC-specific B cells in M167-K-transgenic mice may be due to a very low frequency of M167-VH-region formation during endogenous rearrangement of VH1 to D-JH segments. The somatic generation of the M167 version of a rearranged VH1 gene may occur in less than one of every 105 bone marrow B cells, and a 500-fold amplification of this M167-Id+ B cell would not be detectable by flow cytometry even though the anti-PC antibody produced by these B cells is detectable in the serum of M167-K-transgenic mice after immunization with PC.