Functional significance of the complement receptors on B lymphocytes

Abstract

The functional role of complement receptor (CR+) lymphocytes in antibody responses was investigated. Initially it was found that in the spleens of 6-8-week-old CBA/H mice only approximately 40% of the B cells were CR+. The CR+ and CR- splenocytes were then separated by a recently described fractionation procedure (Parish, C. R., et al., Eur. J. Immunol. 4, 808, 1974) and assayed alone or in combination for their ability to transfer a range of antibody responses to irradiated recipients. All of the antigens studied, irrespective of their structure or T-cell dependence, were capable of activating CR+ B cells to synthesize antibody. However, only repeating determinant antigens, such as horse red blood cells (HRBC) and dinitrophenyl-polymerized flagellin (DNP-POL), were capable of activating CR- B cells, the soluble antigen DNP-flagellin (DNP-MON) being unable to trigger these cells. Repeating determinant nature rather than T-cell dependence appeared to be the factor that determined whether an antigen could provoke the CR- B cells to synthesize antibody, as HRBC and DNP-POL differ widely in their T-cell dependence. The same phenomenon was observed with direct and indirect PFC responses and also with primary and secondary antibody responses. In addition, there was no evidence for collaboration between CR+ and CR- B cells in the induction of antibody responses to the T-dependent antigens, HRBC and DNP-MON. Furthermore, no CR+ helper T cells were detected. It is postulated that complement receptors facilitate T-B interaction by stabilizing the union of soluble antigens with antigen-specific receptors on CR+ B cells. In contrast, repeating determinant antigens can avidly bind to antigen-specific receptors on B lymphocytes without involvement of the complement receptors. Show more