Fig 1: Neutrophils in blood and colostrum exhibit different morphological and functional features. The expression of a mix of surface markers antibodies (CD45, CD11b, CD66b, CXCR2, CXCR4, CD62L, HLA-DR, CD36, CD14, and CD64) was studied by flow cytometry in the cellular fraction of blood and colostrum of healthy mothers withing 5 days post-partum. A–I Comparison of the expression of surface markers in the identified neutrophil population (Cd66b+) of blood and colostrum samples. N = 12, paired t-test. J CXCR4 versus CD62L representative plot of blood and colostrum neutrophils. K t-SNE representation of color-coded population overlays based on blood and colostrum of neutrophils (left), and the neutrophil subpopulations based on CXCR4 and CD62L expression (right). L Comparison of frequencies of CXCR4−CD62L+ and CXCR4+CD62L− populations in both samples. N = 12, Wilcoxon test. M Representative image of Giemsa staining of CD66b+ isolated cells, N = 6 subjects, 20 cells. N Representative immunofluorescence staining of intracellular MPO of CD66b+ isolated cells, N = 5 subjects, 3–5 cells. O Quantification of intracellular granules, N = 5 subjects, 3–5 cells, paired t-test. P Representative transmission electron microscopy (TEM) images of CD66b+ isolated cells. N = 2 subjects, 5–10 cells. Q Quantification of side light scatter of the neutrophil population by flow cytometry. R Phagocytosis in vitro assay on isolated blood and colostrum neutrophils, upon incubation with pHrodo S. aureus bioparticles. N = 5. S Transwell migration assay on isolated blood and colostrum neutrophils. N = 5. Data presented as mean ± SEM. N = 16, paired t-test. Comparisons not reaching statistical significance are not shown