Age-related changes in plasma IgM level after SRBC-stimulation in the rat

The aim of our investigation was to detect age-related changes in the immune system and immune response of the rat in order to establish a system of biological markers of aging in the immune system. Our results demonstrate significant changes with increasing age in the immune system of Sprague-Dawley rats. Immunoglobulin M (IgM) plasma concentrations showed significant age-related differences after immunization with sheep red blood cells (SRBC). An increase in IgM plasma concentration after exogenous stimulation was found only in young and adult animals but not in old ones. Furthermore, we were able to demonstrate an age-dependent decrease in the peripheral blood lymphocyte count (PBL) and the W3/13-cell count, whereas plasma IgM concentration and polymorphonuclear cell count (PMNC) increased with age in the animals between 12 and 32 months of age. Because of these data, we suggest that the observed decline in humoral immune response with age indicates a decline in cell-mediated immunity.