Studies on immune competence in the rat: changes with age, sex, and strain

Reticuloendothelial capacity (determined by colloidal carbon clearance) and cell-mediated immunity (determined by xenograft skin grafts and macrophage migration inhibition in vitro) were studied as a function of age for the first time in male and female Sprague-Dawley rats. The results of all three tests in the female rat indicated that maximal immune competence was reached at the onset of puberty (4 weeks) and, depending on the immune response, immune competence declined significantly with age (4 to 96 weeks). In the male Sprague-Dawley, a similar pattern was found in two out of the three tests (colloidal carbon clearance, xenograft skin grafts). Macrophage migration inhibition in the male was unaffected by age (4 to 40 weeks). Cell-mediated immunity (xenograft skin grafts) was also studied in male and female rats of another strain (Long Evans) as a function of age. Maximal competence occurred at the onset of puberty and declined thereafter.