Mahdy, A. K. H.; ElAbd, H.; Prinzensteiner, M.; Jebens, H.; Sivickis, K.; Bacher, P.; Vogl, T.; Poyet, M.; Franke, A.

Inflammatory bowel disease (IBD) is an idiopathic, immune-mediated chronic inflammatory disease of the gut with two primary clinical forms, Crohn\'s disease (CD) and ulcerative colitis (UC). Several genetic susceptibility variants have been associated with IBD, such as ATG16L, NOD2, and several human leukocyte antigen (HLA) alleles, nonetheless, the actual disease causes remain unknown. Whereas previous findings have shown elevated responses toward fungal antigens in individuals with IBD, e.g., elevated anti-Saccharomyces cerevisiae antibody (ASCA) levels, an exhaustive mapping of immune responses toward fungal antigens remains incomplete. Thus, we analyzed the fungal mycobiome profiled using internal transcribed spacer 2 (ITS2)-sequencing simultaneously with the T cell repertoire of 637 individuals with IBD from the SPARC IBD cohort, which enabled us to identify 31 T cell clonotypes targeting several prevalent members of the gut mycobiome. Subsequently, we developed a novel phage-immunoprecipitation sequencing (PhIP-Seq) library covering 12,000 potential antigens from the proteome of S. cerevisiae and screened for antibody responses in 100 individuals with CD and 60 healthy controls with known ASCA status, enabling us to identify public and private antibody responses against several S. cerevisiae proteins. In conclusion, we corroborated previous findings showing elevated T cell responses against fungal antigens in individuals with IBD and identified multiple antigenic proteins from the proteome of S. cerevisiae that are targeted by the immune system of individuals with and without CD.