Precursors of both conventional and Ly-1 B cells can escape feedback inhibition of Ig gene rearrangement

Experiments with transgenic mice carrying rearranged Ig transgenes have shown that membrane bound Ig molecules cause feedback inhibition of endogenous Ig gene rearrangement. However, this inhibition is never complete. It has been postulated that escape from feedback may be a property of the Ly-1 B cell subset, whereas rearrangement of endogenous Ig genes may be completely inhibited in conventional B cells. This possibility was investigated in transgenic mice carrying a X transgene under the control of the H chain enhancer. It was found that K producing B cells in these X transgenic mice were for the most part, although not exclusively, of the conventional B cell phenotype. Examination of peritoneal exudate cells revealed that a large proportion of Ly-1 B cells also express κ. Adoptive transfer of bone marrow from adult λ transgenic mice, a source of conventional B cell precursors, resulted in the production of relatively high levels of serum κ 2 to 3 mo after transfer into recipient SCID mice. A high proportion of donor B cells in the spleen produced endogenous K protein with or without co-production of λ. It is concluded that precursors of both conventional and Ly-1 B cells can escape feedback inhibition of L chain gene rearrangement.