Phosphorylcholine on isologous red blood cells induces polyclonal but not anti‐phosphorylcholine plaque‐forming cells in mice

It has been demonstrated in the preceeding report (Bach, M. A., Beckmann, E. and Levitt, D., Eur. J. Immunol. 1984. 14: 589) that phosphorylcholine (PC) on the bacterium Streptococcus pneumoniae R36a stimulated polyclonal as well as anti‐PC plaque‐forming cells (PFC) in mouse spleen in vivo. In this study, red blood cells from BALB/c mice (MRBC) were either conjugated with PC, 2,4,6‐trinitrophenyl (TNP) or treated with phospholipase A2 (PLA2) to expose PC on the cell membrane (determined by hemagglutination with the anti‐PC myeloma HOPC8). When BALB/c mice were immunized i.v. with the conjugated or enzyme‐treated MRBC, a significant polyclonal antibody response ocurred (p < 0.05) using PC‐MRBC or PLA2‐treated MRBC, but not with TNP‐MRBC or sham‐treated MRBC. No anti‐PC or anti‐MRBC immunoglobulin‐secreting cells developed after immunization. Repeated immunization with PC‐MRBC resulted in similar levels of protein A PFC after each immunization but no anti‐PC, anti‐MRBC or anti‐PC‐MRBC PFC. Thus, PC on R36a or isologous RBC stimulated increased numbers of splenic plaqueforming cells. In the case of R36a, 10‐25% of these PFC produced antibodies directed towards PC. In contrast, PC‐MRBC or PLA2‐treated MRBC, failed to evoke any anti‐PC antibody responses.