Immunodepression of thymus-independent response to dextran in mouse malaria.

The thymus-independent antibody response to the alpha 1-6 epitope of dextran B512 was depressed strongly during acute non-lethal Plasmodium yoelii yoelii malaria, but not during low-grade chronic Plasmodium berghei infection. In the acute infection, which is self-limiting, the duration of severe immunodepression was short and was seen only in mice immunized at or around the time of peak parasitaemia. Mice primed at this time responded normally to challenge 20 days later: thus the primary exposure to dextran had no apparent tolerogenic effect. Spleen cells from the immunodepressed mice responded well after transfer to non-infected irradiated hosts, and did not interfere with the adoptive response of normal cells; this, and the fact that P. y. yoelii induced immunodepression in T cell-deprived mice, suggested that T suppressors were not involved. Lack of accessory function, and possibly active suppression, by macrophages remain the most probable explanation for the effect of malaria infection on T-independent antibody responses.