Phytohemagglutinin stimulation of enhanced immunoglobulin G production in mice inoculated with type III pneumococcal polysaccharide.

In BALB/c mice previously inoculated intraperitoneally with an immunogenic dose of the T-independent antigen type III pneumococcal polysaccharide, the intravenous administration of the T-cell activating agent phytohemagglutinin P causes a pronounced increase in the number and relative proportion of immunoglobulin G-producing cells. These results, detected by a modified hemolytic plaque assay, were supported by finding increased levels of serum immunoglobulin G anti-type III pneumococcal polysaccharide in the treated mice. A comparable stimulation of immunoglobulin G antibody-producing cells was not induced in phytohemagglutinin P-treated nude mice, indicating that the change in class of the predominant antibody is attributable to the activation by the phytohemagglutinin P of a T-cell population. Under the conditions of these experiments, phytohemagglutinin P also promotes a progressive suppression of the antibody-forming cells during the response to type III pneumococcal polysaccharide.