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Abstract Spleen cells, from BALB/c mice primed with keyhole limpet hemocyanin (KLH), were stimulated with heat‐killed vaccine of rough Pneumococcus pneumoniae R36A (Pn) and/or phosphorylcholine (PC)‐coupled KLH to induce an anti‐PC response in vitro. The response to PC‐KLH was found to be T‐dependent while it is T‐independent to Pn. The antibodies induced with either antigen had similar avidity and expressed the TEPC 15 idiotype exclusively; thus T cell involvement in the response to PC‐KLH failed to alter these parameters of the anti‐PC response. At the precursor cell level, Pn induced small clones with an average size of 10 plaque‐forming cells (PFC), whereas PC‐KLH gave rise to larger clones of 40–50 PFC. This difference in the proliferative potential of PC precursor B cells hinted at the possibility that Pn and PC‐KLH were stimulating different precursors. This was corroborated by the observation that a) when Pn and PC‐KLH were added to the same cultures a synergistic effect was seen, i.e. the number of plaques was greater than the sum of the responses induced by each antigen, and b) in microcultures, under conditions limiting B cells only, Pn plus PC‐KLH induced a higher fraction of responding wells than either antigen on its own. We postulate that Pn and PC‐KLH stimulate subpopulations of PC precursor cells which are T‐independent and T‐dependent, respectively.
Quintáns et al. (1976) studied this question.