Infrequent utilization of the immunoglobulin heavy chain variable region(s) identical or closely related to that of MOPC315 myeloma protein in the functional V region formation in B-precursor cell lines.

We raised anti-VH315 antibodies by immunization of rabbits with VH315 fragments, the variable portions of the immunoglobulin heavy chains of MOPC315 myeloma protein. Inhibition radioimmunoassay using various immunoglobulins as inhibitors showed that the anti-VH315 antibodies specifically reacted with the variable portions of the heavy chains of MOPC315 myeloma protein. When the variable region (VH) gene of the heavy chains was cloned and sequenced from the cells producing the heavy chains detected by the anti-VH315 antibodies, the VH gene was closely related (82% homology at amino acid level) to the VH gene of MOPC315. When we examined the frequency with which the variable region(s) detected by the anti-VH315 antibodies were expressed in eight Ignull Abelson virus-transformed cell lines (DJ/DJ or VDJ-/DJ), which were able to generate functional V regions during culture, only one cell line, AT8-1, produced a small number of intracytoplasmic mu-positive cells (VH315+ cells) stained by the anti-VH315 antibodies. The percentage of the total number of the VH315+ cells to the total number of intracytoplasmic mu-positive cells was 0.91% in AT8-1. In the remaining seven cell lines, no VH315+ cells were detected. In the present study we estimate, for the first time at the individual cell level, the frequency of the utilization of the heavy chain variable region(s) identical or closely related to that of MOPC315 in the functional V region formation during early B-cell development.