Studies on the pathogenesis and serodiagnosis of systemic candidiasis
A mouse model was used to study the pathogenesis of systemic infection by the opportunistic pathogen Candida albicans. Using this model it was demonstrated that C. albicans yeast cells were more pathogenic for mice than hyphal forms. Polymorphonuclear leukocytes were shown to be important in resistance to systemic infection by C. albicans. Studies on conditions which promote germination of C. albicans yeasts showed that maximum numbers of yeast cells produced germ tubes when incubated in tissue culture media at 37°C, by 2 hours. A comparative ultrastructural examination of yeasts, germ tubes and hyphal forms demonstrated marked differences in the thickness and organisation of the cell walls between these forms. Furthermore, germination of C. albicans yeasts was shown to be accompanied by significant release of cell wall antigens. In vitro interactions between mouse polymorphonuclear leukocytes and C. albicans yeasts, germ tubes and hyphae in the absence of serum were examined. Mouse neutrophils were found to adhere readily to the surface of germ tubes and hyphae but not yeasts. This adherence resulted in damage of the fungus. Studies on the degradation of killed C. albicans yeasts following phagocytosis by murine macrophages in vitro, showed that progressive removal of yeast cell wall layers occurred. This was followed by dissolution of the cytoplasmic contents. During this process, cell wall and cytoplasmic antigens were released into the surrounding medium. An enzyme linked immunosorbent assay was developed to measure IgM, IgA and IgG class antibodies to C. albicans mannan and cytoplasmic antigens in patient's sera, and was shown to have diagnostic potential for candida infection. In particular, use of this assay to monitor the kinetics of antibody levels to these antigens was found to be of diagnostic value for immunocompromised patients at risk of candida infection. Finally a number of monoclonal antibodies were produced to C. albicans cytoplasmic proteins and have been partially characterised.