Lymphoproliferative responses in diet-restricted and aging Sprague-Dawley rats.

Immunological effects of aging and dietary restriction (i.e., chronic underfeeding without malnutrition) were investigated in male CFY Sprague-Dawley rats. From weaning, diet-restricted animals were given the amount of food that maintained their body weights at approximately 50% of age-matched ad libitum controls. Cells from the spleen, Peyer's patches, brachial/axillary lymph nodes, and mesenteric nodes of 12- and 20-month-old rats were tested in vitro against the T-cell mitogens phytohaemagglutinin and concanavalin A, and the B-cell mitogen Salmonella minnesota lipopolysaccharide (with dextran sulphate). No clear boosting effect of dietary restriction nor age-related decline in T- or B-cell response was observed when a standard foetal bovine serum supplement was used. In general however, serum from diet-restricted rats supported better proliferative responses than serum from age-matched controls, suggesting that dietary restriction may promote lymphocyte proliferation by an indirect mechanism. A feature of this study was the variation in phenotype and immune responsiveness among closely related animals. Thus in an outbred population, any beneficial effects of dietary restriction upon immune responses could be outweighed by variation among individuals.

Failure of dietary restriction to enhance cytolytic and chemiluminescent activity of peritoneal exudate cells from ageing rats.

Investigations into the cytolytic activity of peritoneal macrophages from male Sprague-Dawley rats (activated in vivo with Corynebacterium parvum) utilised SV40-3T3 and L-929 target cells in a 72 h [3H]thymidine release assay. The dietary restricted rats under test were given a measured amount of food from weaning sufficient to maintain their body weights at approximately 50% of age-matched controls fed ad libitum. Cytolytic activity was similar in the two dietary groups at both 13 and 21 months of age, nor were chemiluminescent responses of peritoneal cells to latex or zymosan particles affected by the dietary restriction. No differences were seen in the effectiveness of zymosan particles opsonised with serum pooled from dietary restricted versus control rats in stimulating chemiluminescent responses by standard preparations of peritoneal cells, and concentrations of serum C3 and IgG appeared to be unchanged by the dietary regime.