Ontogeny of the Immune Response

Abstract

Three principal points emerge from this brief examination of immunogenesis in the mammalian fetus. The first is that the fetus of at least some species may engage in immunologic responses if suitably stimulated with antigen. Whether maturation of immunologic competence is merely the by-product of some more general biologic development or whether it constitutes a distinct biologic function of its own remains to be established. Second, the fetus does not appear to develop its immunologic competence simultaneously with respect to all antigens. It recognizes and responds specifically to some of them very early in gestation, to others only later, and to several antigens only some time after birth. The nature of this apparent step-wise maturation is not clear, but its existence poses interesting theoretical questions. Finally, the acquisition of immunologic competence presents the fetus with an efficient mechanism of defense and, at the same time, with a disease-producing mechanism. Certain organisms may only cause disease when they can stimulate an immune response. Immunologic nonreactivity to otherwise pathogenic agents may render them innocuous to the host. The possibility that the mother might also respond to antibody formed by the fetus in a manner detrimental to fetal well-being is another indication of the broad pathobiologic implications of the development of immunologic responses by the mammalian fetus.