Induction of light chain expression in a pre-B cell line by fusion to myeloma cells

Pre-B cells, the first cells in the B-lymphocyte differentiation pathway which express immunoglobulin1, have recently been shown to express cytoplasmic μ heavy chain (H) but not light chain (L)2,3. If, as is believed, pre-B cells are the precursors of immature B lymphocytes, which express surface IgM4–7, the differentiation of pre-B cells to immature B lymphocytes must be accompanied by the expression of light chains. In this case, it should be possible for the progeny of a single pre-B cell to express a variety of light chains in association with the same heavy chain. We have tested this hypothesis by hybridizing a pre-B cell line 18–81 expressing only cytoplasmic μ chains8with variant myeloma cells which do not express light chains. Hybridization of B-lymphoma cells with myeloma cells usually produces a hybrid with the phenotype of the more differentiated parent9–11. In this case, the fusion resulted in the induction of light chain expression from the 18–81 genes and we have been able to demonstrate that independent hybrids express different light chains, in accordance with the hypothesis that a pre-B cell committed to expression of a single μ heavy chain can generate progeny expressing different light chains2,12.