Evidence that the fourth component of complement (C4) is carried on a high proportion of normal guinea-pig B lymphocytes.

The fourth component of complement (C4) has been demonstrated on the cell membrane of guinea-pig B lymphocytes isolated from blood, lymph nodes and spleen. In lymph nodes, at least, the C4-positive cells also carry receptors for C3 and most bind IgG-Fc. Few, if any, T lymphocytes have detectable C4. Resynthesis of cell-surface C4 could not be shown following in vitro culture of lymphocytes stripped of C4 by proteolytic enzymes, and it is likely that the C4 is passively acquired in vitro from tissue fluids, possibly by a mechanism similar to that involved in the binding of C4 (Chido and Rodgers determinants) to human erythrocytes.