Phenotype of T cells, their soluble receptor levels, and cytokine profile of human breast milk.

Human breast milk has important immunoprotective and immunosuppressive functions for an infant. The purpose of this study was to extend the phenotype of milk cells and to measure soluble T cell receptor levels and cytokines in milk, and to compare these with neonatal and adult blood. Milk T cells had a more equivalent CD4:CD8 ratio than blood; milk CD4 T cells mainly expressed the CD45RO (antigen primed/memory) phenotype; milk CD8 cells had an equivalent CD11b:CD28 suppressor:cytotoxic phenotype; and milk T cells had 2-3-fold higher percentages of activated CD4 IL-2R and CD8 HML-1 or CD8 VLA-1 cells than blood. Soluble IL-2R, CD4 and CD8 concentrations were lower in milk than adult blood, although relatively increased when compared to the lower T cell concentration in milk. Breast milk contained high levels of IFN-gamma but low levels of other measured cytokines compared to blood. These distinct differences of T cells and their soluble products are likely to influence an infant's immune system.