Human milk contains proteins that stimulate and suppress T lymphocyte proliferation
The modulatory effect of human milk proteins from colostrum and late milk on the proliferative response of human T lymphocytes activated by mitogens (OKT3 and leucoagglutinin from Phaseolus vutgaris) and alloantigens was studied. High concentrations (10‐100 μg/ml) of crude colostral milk proteins had an inhibitory effect on T cell growth while low concentrations (0.1‐1 μg/ml) enhanced T cells growth. In contrast, proteins from late milk did not inhibit T lymphocyte proliferation while the enhancing effect was retained. Colostrum was fractionated by ammonium sulphate precipitation and gel filtration on sepharose 6B. The inhibitory activity was recovered in a protein fraction containing Iactoferrin as its major component. Lactoferrin was. however, not responsible for the observed inhibition. On the contrary. lactoferrin in most cases augmented the proliferative response induced by polyclonal activators. The inhibitory activity was found to bind coneanavalin A‐sepharose suggesting an association with glycoprotein. Inhibitory fractions contained glycoproteins of the following molecular sizes26, 74/76 (doublet),84, 145 and 160 kD under reducing conditions. The inhibitory effect appeared to be lymphocyte specific since the active fraction did not inhibit the growth of tissue culture cells (I‐leLa cells and human fibroblasts) or bacteria. Furthermore, the fraction was not toxic for lymphocytes. The inhibitory colostrum factor may prevent the newborn from overreacting immunologically against the environmental antigens encountered at birth.