Fig 1: MHC mediates IgA response against commensals.(a) Flow cytometry (F.C.) was used to quantify multiple immune parameters within the PPs of MHC congenic animals. A heatmap is used to summarize results of immune phenotyping experiments. Heatmap depicting relative abundances of cell subsets (red=more abundant, green=less abundant). Gray boxes represent no significant differences among genotypes for a given cell subset based on the results of a one-way ANOVA (P>0.05). (b) Data sets comparing discriminating immune phenotypes (H2bb n=15; H2dd n=14; H2kk n=15). Data represent pooled results of three replicate experiments. Data from H2-matched C57BL/6 (H2bb) mice (n=6) are provided for comparison against H2bb BALB/c congenics. (c) Abundance of IgA+ plasmablasts in the siLP was enumerated via flow cytometry (H2bb n=7; H2dd n=6; H2kk n=8). (b,c) Representative F.C. plots are provided to illustrate gating strategy. (d) The abundance of faecal IgA antibodies was measured by ELISA (H2bb n=11; H2dd n=11; H2kk n=11). Data represent pooled results of two replicate experiments. (e) The relative amounts of faecal bacteria bound by IgA was enumerated via flow cytometry among cohorts of H2bb (n=8), H2dd (n=8), and H2kk (n=7) animals. Representative F.C. plots illustrate assay specificity by demonstrating a low incidence of false-positive events recorded in IgA-deficient RAG1-/- control animals. Data represents pooled results from two replicate experiments. (f) The number of unique PP-derived CDR3 amino acid sequences (from IgH chain) observed per sample in each immunoglobulin repertoire rarified to a depth of 1,250 sequence observations per sample. Plots represent pooled data from all three genotypes. (g) Heatmap showing IgH variable family usage among genotypes. For each repertoire, sequence abundance per variable region family is normalized across row via Z-score. Gray cells indicate that a variable family was absent in all three genotypes within a given Ig repertoire. (h) The number of unique IgA and IgG CDR3 amino acid sequences (pooled) observed among genotypes rarified to a depth of 1,250 sequence observations per sample (H2bb n=4; H2dd n=4; H2kk n=4). (i) The mean affinity maturation index for all unique IgA and IgG sequences within a given genotype. Error bars represent s.e.m. (b,c,d,e,f,h,i) Bars represent means. Asterisks denote results of two-tailed unpaired Student's t-tests (****P<0.00001; ***P<0.001; **P<0.01; *P<0.05). NS, not significant.