IDENTIFICATION OF IL-7-DEPENDENT BONE MARROW-DERIVED THY-1-B220- LYMPHOID-CELL CLONES THAT REARRANGE AND EXPRESS BOTH IG AND T-CELL RECEPTOR GENES

Bone marrow stromal cell lines and lymphoid cell lines were co-established from the Whitlock-Witte type of long term liquid cultures of MRL/1 and C57BL/10 (B10) (Thy-1.1) bone marrow cells. The present study investigates the immunologic nature of parental and cloned lymphoid cell lines. Both strains of parental lines and their clones did not grow alone but proliferated on the monolayers of co-established parental stromal cell lines from a syngeneic or alternative strain. When various lymphokines or cytokines were tested for their capacity to support the growth of these lymphoid cell clones, only IL-7 could substitute for the growth-promoting function of stromal cells. These IL-7-dependent clones expressed neither Thy-1 nor B220 Ag. However, all of them from two strains were found to rearrange synchronously H chain of Ig as well as gamma-chain of TCR genes. Some of the clones transcribed a mature size of IgH mRNA. Co-expression of mRNA for lambda-5 but not for IgL chain (kappa, lambda) genes resulted in the generation of cell surface mu-chain in these clones. Other clones expressed a smaller size of IgH MRNA without exhibiting surface mu-chain. Irrespective of the differences in IgH rearrangements and its mRNA expression, a mature size TCR-gamma mRNA was detected in all of the clones. Thus, these results demonstrate the existence of untransformed (IL-7-dependent) immature lymphoid cells rearranging both Ig and TCR genes. Their unique features concerning cell surface markers (B220--mu+), specific growth factor requirement, and various modes of Ig/TCR gene rearrangements are discussed in the context of early lymphoid development.