Inducible proteinase of Candida albicans in diagnostic serology and in the pathogenesis of systemic candidosis.

The extracellular acid proteinase of Candida albicans was purified from culture filtrates by a single-column chromatographic step. The purity of the enzyme and its unique antigenic properties were confirmed by polyacrylamide-gel electrophoresis and by reaction with homologous and heterologous anti-sera. The purified enzyme (PP), which was a carboxyl proteinase, contained mannan as an integral part of the molecule. C. albicans proteinase was detected in experimental candida kidney lesions by indirect immunoflourescence. Precipitating antibodies to PP and to cytoplasmic extract (CE) were detected in sera from rabbits with chronic, experimental, systemic candidosis; however precipitins to PP were not found in sera from infected rabbits in which tissue invasion was prevented by antifungal treatment. In retrospective tests with sera from healthy subjects and from patients with and without proven systemic candidosis a qualitative distinction between true and false-positive precipitins to PP was not found; however, whereas 72% of sera from proven cases of deep-seated candida infection had anti-PP titres greater than 4 and greater than or equal to anti-CE titres, these same quantitative criteria were met by only 15% of sera from patients for whom information of a diagnosis of candidosis was not available. The purified proteinase was therefore a more specific antigen than the widely used cytoplasmic extract for detection of antibodies in cases of candidosis.