The determination of numbers of T and B lymphocytes in the blood of children and adults by the direct immunofluorescence technique

Lymphocytes in the peripheral blood of sixty-five children ranging in age from newborns to 14-year-olds and twenty-one adults were studied by the direct immunofluorescence technique for B- and T-membrane determinants, with a GaHu–Fab fluorescein isothiocyanate (FITC) conjugate as a B-cell marker and a tetramethyl rhodamine isothocyanate (TRITC) labelled horse anti-human T-cell conjugate (ATC) as a T-cell marker. The ATC was prepared from a commercial horse anti-human thymocyte IgG fraction and made specific for human T lymphocytes by means of extensive absorption with all kinds of human blood cells. Lymphocytes were also tested for E-rosette formation with sheep red blood cells (SRBC). In adults, an average of 79% of peripheral blood lymphocytes reacted with the ATC, 14% with the anti-Fab conjugate, 2% with both conjugates and 5% with neither of the conjugates. An average of 76% of peripheral blood lymphocytes (PBL) formed E rosettes. Relative numbers of fluorescent B and T lymphocytes in blood from children showed no significant differences as compared to adults. The percentage of E rosettes in cord blood was lower than in any of the other age groups studied, but only in comparison with the 3–12-month-old age group was the difference significant ( P