Activation of antigen-specific suppressor T cells by the intravenous injection of soluble blood-stage malarial antigen.

The regulation of delayed-type hypersensitivity (DTH) to soluble antigens derived from blood-stage parasites was investigated. DTH responses to soluble blood-stage malarial antigen were induced by subcutaneous (sc) sensitization in the flanks and elicited by ear challenge with the same antigen 6 days later. Adoptive transfer studies revealed that T cells of the L3T4+ phenotype were mediating this response. When a high dose of malarial antigen was injected intravenously (iv) prior to sc sensitization, immunosuppression of DTH resulted. The degree of immunosuppression was dependent on the dose of antigen injected iv and the time at which it was administered prior to sc sensitization. Immunosuppression was antigen-specific and mediated by Lyt-2+ splenic T cells.