Candida is among the leading causes of nosocomial bloodstream infections, and a significant proportion of candidemias are due to non-albicans Candida species. Natural antibodies reactive with cell wall mannan or glucan play an important role in host immune defense mechanisms. We have previously demonstrated an intrinsic resistance of C. albicans mannan to complement activation in the absence of antibody and a requirement of antibody to initiate complement. The purpose of this study was to characterize the role of natural antibodies in complement activation by non-albicans Candida species. Similar to C. albicans, yeast cells of non-albicans Candida species; C. glabrata, C. tropicalis, C. parapsilosis, C. guilliermondii, C. kefyr, and C. krusei, were found to react with natural antibodies present in normal human serum (NHS) but vary in quantity and apparent affinity. Next, C3 deposition onto yeast cells through either the classical or alternative pathway was assessed in NHS and in yeast adsorbed NHS; cell-bound C3 was quantified by flow cytometry and visualized by fluorescence microscopy. C3 deposition onto the yeast cell surface in NHS was rapid and uniform for all species. Treatment of NHS with EGTA to limit complement activation to the alternative pathway delayed initiation of C3 deposition. Yeast adsorption of NHS to remove natural antibodies further hindered C3 accumulation on the yeast cell surface. The ability of non-albicans species to activate the alternative pathway in the absence of antibody was assessed by a serum free assay and by factor B depleted serum. C. kefyr activated the alternative pathway independent of antibody, which indicates the cell surface is not inherently resistant to C3 deposition. Therefore, most non-albicans Candida species require natural antibodies to activate complement, but C. kefyr has a unique cell surface that is able to spontaneously initiate C3 deposition in the absence of antibody.
|School:||California State University, Long Beach|
|School Location:||United States -- California|
|Source:||MAI 49/05M, Masters Abstracts International|
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