Membrane-associated immunoglobulin determinants on bone marrow and blood lymphocytes in the pediatric age group and on fetal tissues.

Lymphocytes from bone marrow and blood of infants and children and from various tissues of seven fetuses between 13 and 25 weeks of gestational age were studied by immunofluorescence for the presence of membrane-associated immunoglobulins. Cells with mu and delta determinants prevailed, and these immunoglobulins were usually present on the same cell. The bone marrow specimens of all age groups contained more mu-positive cells without delta determinants than did the samples from the peripheral blood. Such mu(+)delta(-) cells were also found in tissues of young fetuses. These cells were postulated to represent the first stage of B cells displaying Ig receptors. Other tests with double staining showed that cells with delta determinants, but without the presence of other H chains, are rare, if they exist at all. This finding supports the idea that the role of IgD could be one of regulation of antibody secretion rather than of antibody activity. The number of cells that displayed alpha determinants was first observed to rise after birth, and only in the bone marrow, where it reached an average maximum of 16%. The relative number of such cells in the blood never exceeded a few percent.