Immunosuppression in murine malaria: a soluble immunosuppressive factor derived from Plasmodium berghei-infected blood.

Mice infected with Plasmodium berghei have a depressed immune response to a variety of antigens. We report the extraction, purification, and characterization of a soluble immunosuppressive substance derived from P. berghei-infected mouse blood. A crude extract, prepared by solubilization of infected erythrocytes in a Parr cell disruption bomb, reduced the anti-DNP PFC response of mice injected with the extract 1 day before immunization. Purification of the immunosuppressant was accomplished by precipitation with 50% saturated ammonium sulfate followed by chromatography on Sephadex G-150 in the presence of 6 M guanidine hydrochloride. The immunosuppressive activity was recovered in the last fraction eluted from the Sephadex G-150 column that contained low m.w. components. The activity was abrogated by trypsin digestion, but not by periodate oxidation. Volume for volume, the purified immunosuppressant had a 100-fold greater activity than the crude extract from which it was derived. It suppressed the response to the T-dependent antigens DNP-KLH and SRBC, but not to the T-independent antigen DNP-Ficoll.