title: Ontogeny of immunity in man.
abstract: We have reviewed selected aspects of recent findings in the ontogeny of immunity in man. For obvious reasons, constraints placed on experimental work with human subjects, albeit deceased foetuses, limit the work to in vitro studies. Nevertheless, a number of novel and important concepts have emerged. First, as in lower animals, lymphoid development of the foetal thymus in general precedes the development of immunocompetence in peripheral lymphoid tissues. A striking exception to this rule is the finding of cells in early foetal liver which respond to allogeneic cells in the mixed lymphocyte culture some weeks before lymphoid organization of the thymus. In addition, the response of foetal cells to allogeneic cells in the mixed lymphocyte reaction (MLR) precedes the response to phytohaemagglutinin (PHA), a stimulant with relative T cell specificity. The use of markers for T cells to map the emergence of this class of lymphocytes correlates well with various functional attributes of T cells in in vitro culture systems. B cells emerge first in foetal liver at about 9 weeks' gestation, but formation of immunoglobulin by the foetus occurs at very low levels until after birth. There is a suggestion that progression from IgM to IgA synthesis occurs during human foetal lymphoid development. Taken as a whole, these data suggest a rather remarkable and perhaps unexpected degree of cellular and potential humoral immunocompetence at early stages of feotal development in man.
mesh_terms: D000818:Animals; D000917:Antibody Formation; D001402:B-Lymphocytes / Q000276:immunology; D001666:Binding Sites, Antibody; D005075:Biological Evolution; D004247:DNA / Q000096:biosynthesis; D005333:Fetus / Q000276:immunology; D005865:Gestational Age; D006801:Humans; D007104:Immune Adherence Reaction; D007109:Immunity; D007111:Immunity, Cellular; D007070:Immunoglobulin A / Q000096:biosynthesis; D007075:Immunoglobulin M / Q000096:biosynthesis; D007231:Infant, Newborn; D037102:Lectins / Q000494:pharmacology; D008213:Lymphocyte Activation; D007959:Lymphocyte Culture Test, Mixed; D013601:T-Lymphocytes / Q000276:immunology
chemical_list: D007070:Immunoglobulin A; D007075:Immunoglobulin M; D037102:Lectins; D004247:DNA