Influence of surrogate L chain on D sub(H)J sub(H)-reading frame 2 suppression in mouse precursor B cells

D sub(H)J sub(H) rearrangements start in progenitor and precursor B cells and occur in three reading frames (rf). A strong bias for rf I has been noticed in murine and chicken antibodies, while the representation of rf II has been found suppressed both in peripheral as well as in precursor B cells. H chain gene loci D sub(H)J sub(H) rearranged in rf II are potentially capable of expressing a truncated D sub(H)J sub(H)C sub( mu ) protein on the cell surface. In this paper we show that suppression of rf II is not yet established in c-kit super(+) CD43 super(+) IL-7/stromal cell-reactive pre-B I cells of fetal liver at day 15 of gestation, but becomes established when such precursor cell populations are expanded in vitro on stromal cells in the presence of IL-7. These experiments suggest that surrogate L chain is involved in rf II suppression. This may happen by inhibition of proliferation of pre-B cells expressing a complex of D sub(H)J sub(H)C sub( mu ) protein and surrogate L chain.