Mechanisms by which hapten conjugates of pneumococcal polysaccharide interfere with the challenge of anti-hapten memory cells.

Incubation of trinitrophenylated hemocyanin (TNP-KLH)-primed spleen cells with microgram amounts of 2,4-dinitrophenyl (DNP) or 2,4,6-trinitrophenyl (TNP) conjugates of pneumococcal polysaccharide type 3 (SIII) for as little as 5 min at 4 degrees C results in a specific "block" of the 19 S and 7 S adoptive memory response to TNP-KLH. This hapten-SIII-induced block of anti-hapten memory B cell responsiveness seems to be an example of specific receptor blockade. The block is specific and can be prevented by simultaneous incubation of the primed cells with hapten-protein conjugates which presumably compete with the hapten-polysaccharide for attachment to the B cell surface via anti-hapten Ig receptors. Removal via capping of these Ig receptors by exposure of TNP-KLH-primed memory cells to rabbit anti-mouse Fab serum for 45 min at 37 degrees C renders these cells refractory to the blocking effect of hapten-SIII. Once the hapten-SIII has attached to the memory cells, these blocked cells can be "rescued" (i.e. returned to a state of responsiveness) by incubating these cells with either mouse anti-SIII at 37 degrees C or rabbit anti-DNP serum at 4 degrees C. Since a papain digest of the IgG fraction of rabbit anti-DNP did not rescue the cells while the intact IgG did, a capping off of the TNP-SIII was proposed as the mechanims for this return to responsiveness of the hitherto blocked cells. A rescue was not seen by treatment of recipient mice with such B cell mitogens as dextran sulfate, endotoxin or purified protein derivative of tuberculin.