The secretion of aspartyl proteinase, a virulence enzyme, by isolates of Candida albicans from the oral cavity of HIV-infected subjects

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Abstract
Prevalence, serotype and in vitro secretion of aspartyl proteinase, a virulence enzyme, were studied in Candida isolates from the oral cavity of 337 HIV-infected subjects. Controls were 95 age-sex-matched HIV- (seronegative) subjects, belonging to either HIV-risk categories (47) or to the normal, general population (48). Fungi were isolated from 155 HIV+ subjects. C. albicans was the most prevalent species (85.8% of all isolates). 94.6% of C. albicans isolates were serotype A and all were agglutinated by a monoclonal antibody (AF1) directed against a major mannoprotein immunogen of the candidal cell wall, confirming previous results with C. albicans isolates from non-immunodeficient subjects. With regard to the stage of HIV infection, there were no statistically significant differences in the incidence of oral Candida carriage between asymptomatic (stage II) HIV+ and HIV- subjects, and between stage II and lymphadenopathic (stage III) individuals. Also, the low (3.8%) incidence of oral candidiasis in the subjects of the latter stage was insignificant with respect to stage II subjects. However, the incidence of C. albicans in stage IV (AIDS) subjects (46.8%) was significantly higher than in all other subjects, and in almost all cases, fungal isolation was accompanied by oral thrush and lower CD4+ lymphocyte counts (< 400 × 10°/L). All isolates of C. albicans were proteolytic in vitro, as assessed by scoring the proteinase activity on BSA agar and monitoring the secreted proteinase antigen by a highly sensitive (1 ng) and specific immunoenzymatic assay. However, by both methods, the isolates from subjects at stages III and IV of infection produced more secretory proteinase than the isolates from either HIV+ asymptomatic subjects or HIV- controls. The differences could not be attributed to particular culture media or source of Candida isolation (carriage versus active infection). Thus, the isolates of C. albicans from advanced HIV infection are serologically similar but more proteolytic than the isolates from earlier stages of HIV infection or those from HIV-uninfected subjects. The apparently higher virulence of C. albicans from AIDS subjects may represent a co-factor in determining and/or aggravating oral candidiasis in these patients.

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