Microbial proteins shape the development of Fab-dimerized glycan-reactive antibodies that target glycosylated HIV-1 envelope

Fab-dimerized glycan (FDG)-reactive antibodies (Abs) bind a myriad of glycosylated pathogens in a glycan-dependent manner. We defined microbial proteins that bound FDG-reactive monoclonal (m) Abs from human HIV-1 infection (2G12), HIV-1 seronegative human (DH1005), and Simian-HIV (SHIV)-infected (DH851.3) and HIV-1-vaccinated (DH717.2) rhesus macaques. FDG mAbs bound diverse proteins in Candida albicans lysates, including 1,3-beta-glucanosyltransferase PGA4 (PGA4). Recombinant PGA4 was bound by FDG-reactive mAbs in a predominantly glycan-dependent manner, and tetrameric PGA4 induced calcium flux in a Ramos B cell line expressing DH1005 IgM BCR, suggestive of B cell activation. Additionally, we identified multiple bacterial proteins in human stool-derived intestinal microbiota whole-cell lysates that bound FDG-reactive mAbs, including the Pseudomonas aeruginosa strain XcpQ protein. Recombinant XcpQ was also bound by FDG-reactive mAbs in a glycan-dependent manner. These data provide insights into microbial factors that may contribute to the induction and development of this unique category of glycan-reactive antibodies.