CD5 is a potential selecting ligand for B cells surface immunoglobulin framework region sequences

Abstract

In rabbits nearly all B lymphocytes express the glycoprotein CD5, in contrast to mice and humans, where only a small proportion of B cells express this molecule (Raman, C., and K.L. Knight, 1992, J. Immunol. 149: 3858- 3864). CD5 B cells appear to develop early in ontogeny and be maintained throughout life by self-renewal. The function of CD5 on B cells is still unknown. We showed earlier that 'positive' selection occurs during B lymphocyte development in the rabbit appendix. This selection favors B cells expressing surface immunoglobulins with V(H)a2 structures in the first and third framework regions (Pospisil, R., G.O. Young-Cooper, and R.G. Mage, 1995, Proc. Natl. Acad. Sci. USA, 92:6961-6965). Here we report that F(ab')2 fragments, especially those bearing V(H)a2 framework region determinants, specifically interact with the B cell-surface glycoprotein CD5. This interaction can be inhibited by anti-CD5 antibodies. Furthermore, immobilized F(ab')2 fragments selectivity bind CD5 molecules in appendix cell lysates. Interactions of V(H) framework region structures with CD5 may affect maintenance and selective expansion of particular B cells and thus contribute to autostimulatory growth of autoimmune or transformed cells.