Secretory immune responses in ageing rats. I. Immunoglobulin levels.

Immunoglobulin levels in saliva, serum and gastrointestinal perfusates were measured in groups of ageing CDF (F-344)Cr1BR rats. Four age groups were studied, including: (i) weanling (21-35 days), (ii) adult (3-4 months), (iii) midlife (10-12 months), and (iv) senescent (18-20 months). There was no difference in the mean salivary volume and protein levels in the three older groups of rats. Salivary IgA in the weanling rats was significantly lower, having not yet attained adult levels, while salivary IgG was decreased in the senescent group. No IgM was detected in saliva from any of the animals. Serum IgM was elevated in the midlife and senescent rats. In contrast, serum IgG was significantly decreased in the senescent group when compared to the adult or midlife animals. Significant elevations were noted in serum and intestinal perfusate IgA in the senescent rats when compared to the adult group. While salivary IgA from all groups was shown to be greater than 95% polymeric, only the weanling and senescent groups exhibited a tendency toward predominantly polymeric serum IgA (67-70%). The results define altered immunoglobulin profiles in aged rats in both secretory and systemic fluids, which could affect the immunocompetence of these animals.