Demonstration of T lymphocytotoxic human fetal antibody against maternal T and concanavalin A-inducible adult T cells in cord IgM.

To clarify reasons of the constant presence of IgM in human cord blood, some functions of this immunoglobulin class were analyzed. Cord IgM was collected from cord blood, and the cord IgM F(ab')2 fragment was obtained by trypsin cleavage. Maternal T and adult T cells were stained with fluorescein isothiocyanate (FITC)-conjugated cord IgM and FITC-cord F(ab')2 mu. Cord IgM, unlike cord IgG, bound to about one-third of maternal and one-fourth of adult T cells and killed them, but it killed only a small proportion of the B cells. However, adult F(ab)'2 mu did not kill these cells. Cord T cells were not killed by cord IgM. Thus, it is apparent that cord IgM contains cytotoxic antibodies against maternal and adult T cells. T lymphocytotoxic fetal antibody (TLFA) may be largely responsible for the absence of maternal T cells in cord blood. The percentage of [3H]thymidine incorporation into concanavalin A-induced adult mononuclear cells treated with cord IgM containing TLFA was 56.0 +/- 17.9% (p less than 0.01) and that into pokeweed mitogen-induced cells treated with the cord IgM preparation was 100.3 +/- 17.8% (p greater than 0.05) indicating the possibility that TLFA might kill a certain subset(s) of T cells.