Immunological activities of a Candida albicans protein which plays an important role in the survival of the microorganism in the host.

A protein with an isoelectric point of 4.3 and a relative molecular mass of 43 kDa (p43) was purified from the supernatants of the cultures of pathogenic Candida albicans but could not be detected in the supernatants of cultures of this fungus with pathogenicity previously attenuated after being repeatedly subcultured in vitro. Treatment of BALB/c and C57BL/6 mice with p43 resulted in (i) marked increases in the numbers of splenic immunoglobulin-secreting plaque-forming cells (PFC) with peak responses of immunoglobulin M (IgM) PFC preceding those of IgG PFC, with an isotype restriction pattern of IgG2a > IgG2b > IgG3 > IgG1 > IgM, and (ii) specific immunosuppression of the murine primary immune response against sheep erythrocytes. Immunosuppressive and B-cell mitogenic properties of p43 were quantitatively associated and inversely correlated with susceptibility to C. albicans infection. C57BL/6 mice treated with p43 2 days before inoculation with C. albicans were considerably more susceptible to the fungal infection than untreated mice. The immunobiological and chemical properties of p43 are compared with previously described immunosuppressive and B-cell mitogenic proteins produced by bacteria and viruses, and strategies for immunointervention are discussed.