Holder pasteurization reduces the bacterial binding properties of breast milk–derived IgA. Breast milk samples from four donors were split into two where one half was pasteurized (62.5°C for 30 min) while the other was untreated as a control. IgA was then isolated from both halves and analyzed on our flow cytometric array (Fig. 1 A). (A) Paired Student’s t test (***P < 0.001) of the IgA concentration (mg/ml) of control (blue) and pasteurized samples (red), as measured by ELISA. (B) Paired Student’s t tests comparing control (blue) and Holder pasteurized (red) milk samples from the same donor. Each dot represents a different bacterial taxon. ****P < 0.0001. This figure is an aggregate of experiments on four donor samples.