Cell surface expression of the short immunoglobulin mu chain (D mu protein) in murine pre-B cells is differently regulated from that of the intact mu chain.

Pre-B cells carrying DJH rearrangements in an appropriate reading frame produce a short mu protein consisting of a DJH and the C mu & sequence (D mu protein). We analyzed a D mu-producing Abelson-murine leukemia virus-transformed murine pre-B line, 300-19, and demonstrated that D mu proteins are expressed on the cell surface in association with surrogate L chain proteins (lambda 5 and VpreB). However, when we introduced an expression vector coding for the D mu protein into the null pre-B line P17-27, which produce lambda 5 and VpreB but no Ig molecules, most of the cells did not express D mu proteins on the cell surface although D mu proteins were produced intracellularly. On the other hand, P17-27 brings intact mu chains on the cell surface, when a vector coding for the intact mu chain is introduced. Thus, cell surface expression of the D mu protein has different requirements from that of the intact mu chain. A possible role of the VH protein encoded by germ-line VH transcripts is discussed.