Analysis of human host defense mechanisms against the opportunistic pathogen Candida albicans, using in vitro model systems

Various aspects of neutrophil-Candida interactions were investigated. Serum-free culture filtrates of five Candida species and Saccharomyces cerevisiae were found to contain chemoattractants for human neutrophils and a mouse macrophage-like cell line, J774. The chemoattractant in Candida albicans culture filtrates appeared to act through the formyl peptide receptor (FPR) of neutrophils, since it was also found to induce chemotaxis of Chinese hamster ovary (CHO) cells expressing the human FPR, but not wild type CHO cells. Therefore, we have identified a receptor by which a non-serum dependent chemotactic factor (NSCF) produced by C. albicans induces chemotaxis of neutrophils. J774 cells did not migrate toward the formylated peptides and chemotaxis toward the C. albicans culture filtrate was not inhibited by an FPR antagonist, suggesting that a different receptor mediated J774 cell chemotaxis. The C. albicans culture filtrates also induced neutrophil migration across monolayers of a human gastrointestinal (GI) epithelial cell line, T84, in the basolateral-to-apical direction, but not the reverse, unless epithelial tight junctions were disrupted. This observation suggested that NSCFs produced by C. albicans and other yeast species may influence host-pathogen interactions at the GI mucosa by inducing phagocytic cell infiltration.; The role of beta2-integrins in phagocytosis and killing of C. albicans was confirmed using neutrophils isolated from calves with bovine leukocyte adhesion deficiency (BLAD). BLAD neutrophils displayed decreased phagocytosis and killing capabilities, supporting claims that beta2-integrins are the primary PMN adhesins for C. albicans.; To examine the differences in adhesion of Candida species to human GI epithelium, radiolabeled yeast were allowed to adhere to T84 and Caco2 monolayers. The adhesion to T84 monolayers correlated with the reported prevalence of Candida spp. in the human GI tract and the adhesion to Caco2 monolayers was similar, although C. glabrata displayed greater adherence than other yeast tested. C. tropicalis adhered poorly to both cell lines in contrast to exfoliated buccal and vaginal epithelial cells, suggesting differences in expression of cell adhesion molecules on different epithelial cell types and/or Candida species. Therefore, human intestinal epithelial cell lines are a useful in vitro model system to investigate the initial steps of colonization of the human GI tract.