RAG1 and RAG2 in developing rabbit appendix subpopulations.

The appendix of young rabbits is a site of primary heavy chain variable region-gene diversification and B cell selection. Appendix cells from 6- to 9-wk-old rabbits were stained and sorted for surface CD43 and IgM. We found that the CD43+IgM- and double-negative CD43-IgM- cells contained RAG1 transcripts and RAG2 protein. The presence of RAG gene products in appendix raised the possibility that pro-/pre-B cells were present in young rabbit appendix. Although an early suggestion that RAG2 plays a role in variable region-gene diversification by gene conversion in chicken bursa was not supported by studies of RAG2 protein in this tissue, we produced anti-rabbit RAG2 Abs to determine whether RAG2 protein was present in rabbit appendix, where cells that recently underwent gene conversion are found. We detected RAG2 protein in the four subpopulations of rabbit appendix lymphocytes, distinguished by surface CD43 and IgM markers. The appearance of RAG gene products during different stages of B cell maturation may reflect the function of the young rabbit appendix as a site of both B cell development and diversification.