Detection of circulating antibody in human cryptococcosis by means of a bentonite flocculation technique.

In the past, antibodies to Cryptococcus neoformans have been found infrequently in the serum of patients with systemic cryptococcal infections and, for this reason among others, C. neoformans was long considered to be a poor antigen (1). With the application of newer immunologic techniques, however, anticryptococcal antibodies have been demonstrated in some patients. For example, Vogel and associates using a fluorescent antibody technique found measurable antibody in the serum of 6 of 7 patients with cryptococcal infection. Presumed false-positive reactions occurred in 8 per cent of control serum (2). Pollock and Ward using a capsular polysaccharide hemagglutination test, have reported 2 cases of human cryptococcosis in which circulating antibody was found, although positive reactions were also noted in 21 per cent of 28 control specimens (3). In addition, other serologic methods have demonstrated the presence of a circulating polysaccharide, derived from the cell wall of C. neoformans, in the serum of many patients with cryptococcal meningitis (4-6). Previous work in this laboratory has demonstrated that bentonite particles are sensitive and useful carriers of antigen for the study of serologic reactions (7, 8). In the present report, the serum specimens of 47 patients with C. neoformans infections were studied for the presence of anticryptococcal antibodies by means of a bentonite flocculation technique. In addition, the relationship between serum antibody and circulating cryptococcal polysaccharide was examined in selected patients.