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 (<0·05). In the 3–6-month-old age group, the percentage of fluorescent T lymphocytes was highest and the percentage of fluorescent B lymphocytes lowest, but a significant difference was observed only for the B-lymphocyte percentage compared with the first month of age (<0·02). Up to 2 years of age, absolute values for total blood lymphocytes, fluorescent T and B lymphocytes and E rosettes were significantly higher (<0·001) than in the older age groups and adults. After the second year of life, those values were the same as in adults.