Changes in the proportion and absolute number of T lymphocytes in piglets from birth until after weaning and in adults.

The proportion of T lymphocytes was measured on cytocentrifuged leucocytes prepared directly from whole blood after rosetting with sheep red blood cells in the presence of dextran. This method gave similar results to those obtained with conventional mononuclear preparations assessed in a haemocytometer but had the advantages of simplicity, the small volume of blood required and the ease with which absolute T lymphocyte counts could be estimated. The proportion of T lymphocytes did not change between birth and 12 days after weaning and did not differ from adults. However, the number of T lymphocytes at birth was significantly lower than in adults and rose thereafter to values significantly higher than in adults by 12 days after weaning. A comparison between one-day-old piglets and adults revealed that there was no significant difference in the proportion of either T or B lymphocytes between adults and neonates. However, there was some indication that neonates were deficient in the proportion of T lymphocytes capable of binding sheep red blood cells with high affinity. After examining the alpha-naphthyl acetate esterase activity of rosetted lymphocytes it was concluded that this enzyme was not a reliable marker for pig T lymphocytes.