Cell surface and intracellular expression of two Candida albicans antigens during in vitro and in vivo growth

Intracellular and cell surface expression of two antigenic determinants of Candida albicans was studied by reacting ultrathin sections of the fungus with monoclonal antibodies and locating the sites of antibody-antigen reactions by use of colloidal gold-coupled secondary antibody and electron microscopic techniques. Comparisons were made between fungal cells allowed to develop in vitro and cells (in vivo) recovered from infected mice. Differences between in vitro antigen expression and expression in vivo were particularly noted during early germination events. Antigen expression in vivo appears to be concentrated in deeper cell wall layers and beneath the plasmalemma especially on germ tubes. Cells which develop in vivo and in vitro have antigen associated with an outer flocculent layer and on the innermost cell wall layer of mother cells and hyphae. A middle electron transparent cell wall layer is usually devoid of antigen. Comparison of antigen expression during in vivo growth in early (intraperitoneal) infection versus late disseminated (kidney) disease suggests that both of the antigens are expressed in greater quantity on the surface of germ tubes than on mother cells in kidney tissue as compared to intraperitoneally-grown cells. Results also suggest that at least one of the antigens, which is a substituted mannan, can be found on a lamello-tubular intracellular structure.