Detection of IL-6 in human milk and its involvement in IgA production

A large amount of interleukin-6 (IL-6) was found to be contained in human whey. The concentration of IL-6 in colostrum was significantly higher than that in serum or in milk taken 1 month after parturition. Colostrum contained many more mononuclear cells than late milk. In terms of the proportion of monocytes, T cells and B cells, however, there is no difference between colostrum and late milk. There is a significantly positive correlation between the concentration of IL-6 and the number of mononuclear cells in milk. This demonstrates that IL-6 in whey is derived in part from mononuclear cells. Stimulation of human milk mononuclear cells by Staphylococcus aureus Cowan I in the presence of anti-IL-6 antibody markedly decreased the production of IgA. This suggests that IL-6 contained in milk is closely associated with the local production of IgA in the breast.