Identification of Candida albicans Antigens Recognized by Murine Intestinal IgAs by a Gel-Independent Immunoproteomic Approach.

As part of the intestinal microbiota, Candida albicans can elicit a humoral response in the gastrointestinal tract (GIT) that is mainly directed toward hyphal antigens. This response has been implicated in controlling the invasive form of the fungus and maintaining the yeast as an innocuous commensal. However, the specific targets of this response are still unknown. Here, we used a gel-free immunoproteomic methodology to identify C. albicans gut immunogens. For this goal, we previously obtained specific secreted IgA from mice colonized with C. albicans. Then, secretome and surfome from C. albicans wild-type filaments were obtained and incubated with magnetic beads linked to antimouse IgA antibodies. sIgA targets were immunoprecipitated and analyzed by mass spectrometry. A third sample bearing the C. albicans antigen-sIgA complex was also examined. Those identified proteins that exhibited a higher percentile of relative abundance were considered for further analysis. From those, 35 proteins coincided among the three samples. Remarkably, about 40% of the identified proteins appeared in the databases as uncharacterized. The results were then validated by immunofluorescence assays overexpressing some of the genes identified in a yeast-lock C. albicans mutant. Adhesins such as Als3, Als1, and Hwp1 were corroborated to be IgA targets, as well as the chaperone Ssa2. Therefore, this gel-free immunoproteomic approach has been useful to identify new C. albicans antigens that generate a specific humoral response in the murine gut.