Immunosuppression by avirulent, pseudohyphal forms of Cryptococcus neoformans.

Our previous reports have shown that animals inoculated for 8 weeks with 1 X 10(5) pseudohyphal, avirulent C. neoformans exhibited prolonged survival upon challenge with virulent cryptococci. This paper described a transient phase of immunosuppression which occurs during the initial weeks of the immunization protocol. Animals injected with pseudohyphal organisms had depressed responses to T and B-cell mitogens. In addition, they had lowered responses to immunization with sheep erythrocytes. Both humoral and cell mediated responses were affected.