Heterogeneity in the antibacterial reactivity of breast milk–derived IgA. Donor milk samples (term infants; >37 wk gestational age) were analyzed with our flow cytometric array (Fig. 1 A). (A) Heat map of normalized antibacterial IgA binding affinity of different donors. Hierarchical clustering (Spearman). The range of the normalized values across each row is indicated in the left-hand column. Donor numbers indicated on top of each column. (B) Scatter graph showing the normalized antibacterial IgA binding values for each donor (each color represents a different donor). (C) Scatter graph of the normalized BrmIgA binding to different isolates of E. coli separated according to donors selected from the analysis in A. Donor numbers indicated on bottom of each column. (D and E) A correlation network analysis was performed to describe which antibacterial IgA responses were predictive. (D)  Heat map indicating the level of correlation between different bacteria in our array. Black box drawn around Enterobacteriaceae family taxa. This figure is aggregate of experiments on 33 donor samples. (E) Network diagram indicating significantly correlated antibacterial IgA responses.