STRUCTURE AND BIOLOGICAL-ACTIVITIES OF ACAPSULAR CRYPTOCOCCUS-NEOFORMANS-602 COMPLEMENTED WITH THE CAP64 GENE

The extracellular polysaccharide capsule of Cryptococcus neoformans is a well-recognized virulence fatter, Strain 602 is an acapsular clinic al isolate of unknown serotype which has been widely used in studies o f virulence and host-parasite interactions, In previous studies, strai n 602,vas compared with genetically unr elated related strains of vari ous serotypes because the wild-type equivalent of strain 602 was not a vailable. We created an encapsulated strain, TYCC38-602, by transformi ng strain 602 with the CAP64 gene which was isolated from a serotype D strain. Serological tests and chemical analysis of the major polysacc haride capsule of TYCC38-602 indicated that strain 602 was originally derived from a serotype A strain, Restoration of the ability to produc e a capsule enabled strain 602 to cause fatal infection in mice, where as the acapsular strain 602 remained aviralent. Capsule-restored yeast cells of strain 602 activated the human complement system and bound C 3 fragments in a manner that is characteristic of encapsulated cryptoc occi, In addition, the capsule in TYCC38-602 masked the ability of the organism to induce tumor necrosis factor alpha and subsequent nitric oxide synthase production in primed macrophage-like cells, These resul ts indicate that the lark of capsule in strain 602 is the reason for i ts inability to cause fatal infection. Moreover, the acapsular phenoty pe accounts for differences in various biological activities of strain 602 compared to encapsulated strains, The results also indicate that the gene product of CAP64 does not contribute to serotype specificity of capsules in C. neoformans.