Evaluation of the mitogen-induced proliferation and cell surface differentiation antigens of lymphocytes from pigs 1 to 30 days of age.

A study was conducted to characterize aspects of the immune system in the pig from 1 to 30 d of age. Pigs were killed on d 1 (n = 6), d 18 or 19 (n = 6), and d 27 to 30 (n = 7) of age. Lymphocytes were isolated from the blood, thymus, and spleen. Lymphocyte function was assessed for ability to proliferate as induced by concanavalin A (Con A), phytohemagglutinin (PHA), and pokeweed mitogen (PWM). Cell surface differentiation antigens on the lymphocytes were evaluated for percentages of cells expressing CD2+, CD4+, CD8+, and SLA class II molecules. Responses of lymphocytes from blood, thymus, and spleen to any of the mitogens were relatively low d 1 through 16; the greatest proliferation occurred by d 28. No detectable percentages of the cell surface differentiation antigens were found on d 1 and changes varied with age and organ. The results indicate that the porcine immune system is not fully developed at birth and the expression of cell surface differentiation antigens seems to occur before the lymphocytes have the ability to respond to mitogens.