The effect of cord blood sera on CD69 expression.

We have reported previously that cord blood (CB) sera inhibit T cell proliferation and cytokine production, and have suggested that the microenvironment that CB T cells come from may be responsible for the reduced function of CB T cells. In the present study we analysed the effect of CB sera on the expression of CD69, the earliest activation marker, on T and natural killer (NK) cells. CD69 expression on adult NK cells was higher than on CB NK cells (p<0.05). CB and adult blood T cells presented with a similar proportion of CD69 expressing cells. Incubation of peripheral blood mononuclear cells (PBMC) in the CB sera enhanced CD69 expression on alloactivated T cells (p<0.05). However there was no difference in the CD69 expression within the population of alloactivated adult NK cells. Stimulation of PBMC with phytohaemagglutinin (PHA) in the presence of different sera resulted in higher CD69 expression on T cells incubated with CB sera (p<0.05), but was similar on NK cells. Our former experiments documented similar effect of CB sera on CD25 expression on mitogen and allostimulated T cells. Thus CB sera seem to have similar influences on the expression of activation markers on stimulated T cells within PBMC, implying that there may be a factor(s) within CB sera affecting lymphocyte responses and activation status.