Alterations in antigen-induced DNA synthesis by specifically localizing cells and other lymphoid cells as a function of immunological memory

The effect of prior immunological experience on the antigen-induced DNA synthesis by specifically localizing cells (SLC) and other cells capable of migrating into lymph nodes (nonspecific cells, NSC) has been studied. Prior immunization with a homologous red cell antigen (sheep red blood cells, SRBC) results in enhanced DNA synthesis, relative to controls pretreated with saline, by NSC but not SLC for the first 48 hr following secondary immunization. By 72 hr both SLC and NSC show markedly reduced DNA synthesis, the SLC showing the greater reduction. Prior immunization with the strongly cross-reacting antigen, ox red blood cells (ORBC), shows a similar but milder effect; prior immunization with the non-cross-reacting antigen chicken red blood cells (CRBC) is without effect, though a similar depression of DNA synthesis by both SLC and NSC occurs 72 hr after secondary immunization with CRBC. In the presence of a concomitant secondary reaction to a non-cross-reacting (CRBC) or very weakly cross-reacting (horse red blood cells, HRBC) antigen, DNA syntheses by SLC-SRBC and NSC are depressed to approximately the same extent, suggesting that the greater depression of DNA synthesis by SLC seen in homologous secondary reactions reflects the additive effects of clonally specific and nonspecific suppressive factors. A comparison of the DNA synthesis by cross-reacting (ORBC) and non-cross-reacting (SRBC) SLC in mice given SRBC following preimmunization with ORBC suggests that “educated” SLC are considerably more resistant to the effects of nonspecific suppressors than “naive” SLC. Passively administered antibody, in concentrations that markedly reduced the numbers of direct plaque-forming cells appearing 72 hr after primary immunization, had no significant effect on DNA synthesis by SLC or NSC.