Immunological functions in food-restricted rats: enhanced expression of high-affinity interleukin-2 receptors on splenic T cells

Several immunological functions of B and T cells including IL-2 receptor expression on T cells were measured in 12-month-old Fisher-344 male rats maintained from 6 weeks of age on an ad libitum (AL) or a 40% food-restricted (FR) diet. Direct anti-SRBC plaque-forming cell (PFC) assays revealed a higher response in FR rats than in AL rats when splenocytes were cultured with or without recombinant interleukin-2 (rIL-2). B cell functions were studied by using nylon wool-purified splenic B cells stimulated either with rIL-2, lipopolysaccharide (LPS), or Salmonella typhimurium mitogen (STM) as a thymus-independent antigen. Reserve plaque assay showed no difference between FR and AL rats in the secretion of anti-IgM and anti-IgG antibodies. In addition, no difference was found in proliferation of B cells stimulated by LPS, STM mitogens or rIL-2. Although purified splenic T cells demonstrated an equally proliferative response in FR and AL rats when cultured with concanavalin A (Con A) or phytohemagglutinin (PHA), T cells in FR rats developed higher responses when stimulated with an alloantigen and rIL-2. Time-course studies carried out to measure high-affinity (HA) IL-2 receptor (R) molecules by using purified T cells with rIL-2 and ¹²⁵I-labeled IL-2 revealed a higher expression of IL-2R molecules on T cells of FR rats than on T cells of AL rats at 72 h after culturing with Con A. These results indicate that the increased production of antibody to a T cell-dependent antigen (SRBC) and the enhanced responsiveness to alloantigen are attributable to the greater expression of HA IL-2 on T cells, which may facilitate an increased response to and a higher production of IL-2 in FR rats.