IgA and IgG plasma cell antibodies from HD1–HD3 were tested for reactivity with a panel of nonpathogenic and enteropathogenic intestinal microbes. The data shown are representative for at least 2 independent experiments. (A) ELISA graphs show the reactivity profile (black line) of a representative bacteria-polyreactive antibody (HD2g348) with E. coli, M. morganii, E. cloacae, and E. faecalis. High positive (dashed line, ED38; ref. ), low positive (red line, JB40; ref. ), and nonreactive (green line, mGO53; ref. ) antibodies were included in each assay for comparison. Horizontal lines indicate the cutoff OD405 in each assay. (B) Bar graphs summarize the frequency of bacteria polyreactive antibodies (black) and non-bacteria polyreactive IgA and IgG antibodies (white) in each donor as determined by ELISA as in A. (C) Representative ELISA graphs show the reactivity of E. coli, M. morganii, E. cloacae, and rotavirus-specific IgA and IgG plasma cell antibodies from HD1–HD3. Clone names of bacteria-specific antibodies are indicated in the graphs. Additional high positive (dashed line, ED38; ref. ), low positive (red line, JB40; ref. ) and nonreactive (green line, mGO53; ref. ) control antibodies were included in each assay for comparison. Horizontal lines indicate the cutoff OD405 in each assay. (D) Histograms show binding of E. coli–specific (HD3g76, HD3g144) and M. morganii–specific (HD3g71) antibodies to whole bacteria as measured by FACS. Secondary antibody only (neg. control) was included as control in all assays.