Expression of λ and κ Genes Can Occur in All B Cells and is Initiated Around the Same Pre-B-Cell Developmental Stage

Transgenic mice that carry a λ2 transgene under the control of the VX2 promoter and the Ελ2-4 enhancer (λ2Ελ mice) are described. A high proportion of B cells in the spleen and the bone marrow express the λ transgene on the cell membrane. λ2 protein is synthesized by all λ2Eλ-derived spleen B-cell hybridomas that have retained the transgene, suggesting that all B cells have the ability to express λ genes. Feedback inhibition of endogenous K-gene rearrangement is significant, but not complete. The results are similar to those with transgenic mice expressing the same λ2 transgene under the control of the heavy-chain enhancer (λ2ΕΗ mice). Although the λ2ΕΗ transgene is expressed before the λ2Ελ transgene, feedback inhibition seems to occur at about the same stage of B-cell development, regardless of the timing of expression of the λ transgenes. Apparently, feedback is not necessarily coincident with the assembly of a heavy-chain/light-chain complex in pre-B cells. Expression of λ in the normal fetal liver coincides with the expression of κ; thus, it appears that λ-gene transcription is not delayed. The differential rearrangement of κ and λ genes is discussed in the light of these findings.