Immunological and phenotypic characterization of cell constituents of breast milk

The morphology and immunological phenotype of plastic-adherent cells from human colostrum were studied in an in vitro short-term culture (6–7 days) using antibodies to CD3, CD31, CD34, CD45, CD68, vimentin, and osteocalcin. In 20% of the analyzed cultural flasks, nearly equal proportion of fibroblast-like cells and rounded cells was observed. In the 80% of the flasks, cells of regular shape were detected with the presence of single fibroblasts. The diameter of flattened cells ranged from 10 to 100 μm. All plastic-adherent cells did not express CD3 and showed weak binding (w) to the antibodies against CD31, CD34, and CD45. At the same time, we identified adherent cells that readily bound the antibodies against CD68, vimentin, and osteocalcin. According to the literature data, the CD68 + CD3^–CD31^wCD34^wCD45^w immunological phenotype of the majority of the adherent cells from the colostrum allows them to be classified as monocytes/macrophages. High expression of stromal antigens—vimentin and osteocalcin—in 40–45% of the adherent cells in the culturing medium lacking any osteogenic supplements (β-glycerophosphate, ascorbic acid, and dexamethason) implies the presence of osteoblasts in the colostrum, which differentiate from mesenchymal stem cells under the action of humoral factors contained in breast milk.