Lymphocytes with membrane-bound immunoglobulin (B-lymphocytes) in new-born babies.

Lymphocytes with surface-bound immunoglobulins (B-lymphocytes) were detected in cord blood of normal babies by means of immunofluorescent staining of viable cells. The mean value of Ig-positive lymphocytes was 14·3% (range 5–33%). IgM was found on the highest percentage of lymphocytes (mean 9·7%), but IgG was also found in a considerable proportion (mean 7·9%). IgA was usually not demonstrable. IgG2 was the dominating IgG subclass (mean 7·3%). The data indicate that the Ig on any one cell belongs to a single class or IgG subclass. Very few or no lymphocytes were stained with antiserum against the C-terminal half of the IgG Fc fragment. Ig classes and the four IgG subclasses were usually found on a higher percentage of lymphocytes in the child than in the mother investigated at delivery. The presence of B-lymphocytes in cord blood, together with a marked lack of immunoglobulin-producing plasma cells at birth, may be explained by the B-lymphocytes not yet having differentiated to plasma cells in the absence of antigenic stimuli.