Summary auto-generated
This study investigates how environmental pH affects the expression of serotype-specific antigens in Candida albicans. Researchers used monoclonal antibody B9E and polyclonal antiserum against antigen 6 (IF6) to examine two serotypes under varying conditions. In vitro, serotype A cells showed strong reactivity with both antibodies while serotype B cells showed little to no reactivity. However, in vivo (in kidney abscesses from infected rabbits), serotype B cells unexpectedly expressed serotype A antigens. The key finding was that pH dramatically influenced antigen expression: serotype A cells showed maximum antibody reactivity at pH 4.6, with decreased reactivity at acidic pH values, whereas serotype B reactivity increased at alkaline pH values (7.2-9.5). Chemical characterization revealed the antigens were carbohydrate-based, as they were sensitive to periodate oxidation but resistant to heat, protease, and reducing agents. These results demonstrate that serotype determination in C. albicans is phenotypic rather than genotypic, with environmental pH being a critical modulator of antigen expression. The authors emphasize that standardized pH conditions are essential for accurate serotype classification in epidemiological studies.
Key findings
- pH significantly modulates antigen expression in C. albicans serotypes: serotype A shows maximal reactivity at pH 4.6 while serotype B reactivity increases at alkaline pH (7.2-9.5)
- Serotype B cells express serotype A antigens in vivo (in kidney abscesses) but revert to typical serotype B phenotype when cultured in vitro, indicating antigen expression is phenotypically, not genotypically, determined
- The serotype-specific antigens are carbohydrate-based epitopes resistant to proteases and heat but sensitive to periodate oxidation
- At acidic pH (2.0), serotype A strains lose antigen expression and behave as serotype B, demonstrating that environmental pH can obscure serotype identity
- Precise pH control is essential for accurate serotype determination in clinical and epidemiological studies
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Abstract
B Barturen, J Bikandi, R San Millan, MD Moragues, P Regulez, G Quindos and J Ponton
Departamento de Inmunologia, Microbiologia y Parasitologia, Facultad de Medicina y Odontologia, Universidad del Pais Vasco, Bilbao, Vizcaya, Spain.
The monoclonal antibody (mAb) B9E, which reacts with a cell wall surface determinant of Candida albicans serotype A, and a polyclonal monospecific antiserum against the antigen 6 (IF6) were used to investigate the expression of the antigens responsible for the serotype specificity in C. albicans under different growth conditions. By indirect immunofluorescence, both antibodies reacted with the cell wall surface of serotype A yeast cells and germ tubes grown in vitro but no reactivity was observed with serotype B yeast cells. In some cases, only a weak reactivity restricted to a zone close to the parent yeast cell was observed in serotype B germ tubes stained with mAb B9E. Both antibodies reacted strongly with yeast cells and germ tubes present in kidney abscesses from rabbits infected with both serotypes, but only serotype A yeast cells and germ tubes present in smears from patients with vulvovaginal candidiasis reacted with B9E and IF6 antibodies. The expression of antigens reactive with both antibodies was modulated by the pH of the environment in which the fungus was grown. Both antibodies showed a similar pattern of reactivity when studied with a spectrofluorometer. Serotype A yeast cells showed maximum reactivity when cells were grown on Sabouraud dextrose broth supplemented with yeast extract at pH 4.6. The lowest reactivity was observed in cells grown at pH 2.0. Conversely, the reactivity of serotype B yeast cells increased at alkaline pH values, the highest being in cells grown at pH values of 7.2 and 9.5.(ABSTRACT TRUNCATED AT 250 WORDS)