Assessment of CD2, CD4, CD8 and γδ cell distribution among mononuclear cells obtained from the blood and lymphoid tissues of fetal calves, 0-150-day-old calves and adult cows was the focus of this investigation. The distributions of some of the lymphocyte subsets in peripheral blood showed variation in fetal and maturing calves as well as being markedly different from those observed in adult cows. We provide evidence that as early as 1 month prepartum, fetal calves have a full complement of at least four of the major T-cell subsets found in the normal bovine. In blood, CD2(+) were significantly higher at 1, 30 and 90 days of age, CD4(+) and CD8 cells demonstrated a peak in the fetuses that dropped below adult levels from 1 to 120 days of age, and γδ(+) cells were highest at birth and decreased to adult levels by 150 days of age. Except for the γδ(+) cells, the subsets were significantly higher in lymphoid tissues obtained from fetal and maturing calves than in the mature animals. All four subsets were significantly higher in fetal and young calf splenic tissues. No significant differences were observed in the distribution of the four subsets in thymuses assayed in this study. An interesting pattern was seen in a longitudinal study of T-cell subsets that showed 7-8 day cyclical changes in CD2 and CD4 marked cells in adult peripheral blood.
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