Induction of 19S IgM secretion in a murine pre-B cell line, 70Z/3, by cell hybridization with non-secreting myeloma cells.

Somatic cell hybrids were prepared between the TK-deficient variant of murine pre-B cell line, 70Z/3, cells and the HGPRT-deficient variant of non-secreting myeloma cells. Several hybrid clones which secreted IgM but did not express surface IgM were isolated. LPS stimulation did not induce the expression of surface IgM. SDS-PAGE analysis indicated that the IgM secreted by one of the hybrid clones was a 19S pentamer and that the size of its mu-chains was the same as that of mu-chains from MOPC 104E myeloma IgM. Two-dimensional gel electrophoresis of biosynthetically labeled immunoglobulin showed that the same pattern was obtained with kappa-chains from two hybrid clones and from the LPS-induced 70Z/3 cells. The result showed that cell hybridization could induce L-chain synthesis in the pre-B cell line. Anti-idiotypic antibody against the secreted IgM was prepared and it was shown that the surface IgM expressed on all LPS-stimulated 70Z/3 cells bore the same idiotype. Those results indicated that the specificity commitment has already occurred in 70Z/3 cells.