The influence of poly I: poly C on kinetics of the primary immune response to sheep erythrocytes in the mouse spleen.

In several mouse strains, which exhibited variability in degree of immune responsiveness, concomitant i.p. injection of antigen (sheep erythrocytes) and poly I: poly C enhanced the early rate of increase in antibody plaque-forming cells (PFC) in the spleen. This adjuvant effect of poly I: poly C was most marked in LACA mice and was demonstrable over a range of antigen and polynucleotide concentrations. The double-stranded RNA did not however, affect the number of PFC at the peak of the primary response. Stimulation was dependent on the temporal relationship between antigen and adjuvant administration--injection of poly I: poly C 24 and 48 h prior to antigen causing suppression of humoral immunity. Poly I: Poly C had a progressively more marked enhancing effect on PFC production at high (thymus-independent) doses of erythrocytes. This suggests that its adjuvant action may be mediated via cells other than T cells. Administration of poly I: poly C caused an initial depression followed by stimulation of spleen weight and nucleated cell numbers in sensitized animals. The possible mechanism(s) of action of this polynucleotide adjuvant are discussed in the light of these and other findings.