Ontogeny of B-lymphocytes in the human fetus

Abstract

Cells bearing membrane-bound immunoglobulins, a marker for B-lymphocytes, have been sought in hematopoietic and lymphoid tissues of 11 human fetuses, aged 9.5–23 weeks. B-lymphocytes with membrane-bound IgM and IgG were found in liver from one of two fetuses aged 9.5 weeks; only IgM-positive cells were found in the other. IgA-positive cells were first detected at 11.5 weeks. By 14.5 weeks, the percentage of cells in spleen and peripheral blood staining for each class of immunoglobulin was within the range found in blood from 10 term infants and 36 normal children and adults. A different fluorescent antibody-staining technique was used to detect immunoglobulin-secreting cells in selected fetuses. No cells with cytoplasmic immunoglobulin were found at 14.5 weeks, a time when B-lymphocytes had reached normal adult proportions in spleen and blood. With one exception, a single IgM-positive cell in an 11-week fetus, such cells were not seen before 15.5 weeks and were rare thereafter. It is concluded that B-lymphocyte development begins at about the same time as T-lymphocyte development. The order of appearance of cells bearing different immunoglobulin classes is probably IgM, IgG, and IgA. The temporal consistency of appearance of these cells suggests that their development is an event of normal differentiation rather than one dependent upon random antigenic stimulation.