Mechanisms of Fetal Immune Response

To the Editor: The recent study of Aase et al. (N Engl J Med 286:1379–1382, 1972) showed that almost all pregnant women infected with mumps virus subsequently had offspring who displayed normal cellular immunity but who lacked measurable antibody against mumps virus. Dr. Silverstein, in his covering editorial (N Engl J Med 286:1413–1414, 1972), suggested the possibility that a “theoretical… mode of split tolerance, involving the presence of cellular immunity in the absence of antibody formation” existed in these children. An experimental model of just such a split tolerance now exists. Katz et al. (J Exp Med 134:201, 1971).