SPLENOCYTE SUBPOPULATIONS OF WEANLING COTTON RATS (SIGMODON HISPIDUS) ARE INFLUENCED BY MODERATE PROTEIN-INTAKE

Populations of cotton rats (Sigmodon hispidus) frequently exhibit extreme fluctuations in abundance, which have been attributed to changes in food quality and its possible effect on survival of juveniles. Weanling cotton rats fed low-protein diets experience altered immune-system function. We evaluated the effects of moderate restriction of dietary protein on splenocyte subpopulations of weanling cotton rats and determined the influences of onset of protein restriction at an earlier age compared with previous studies. Weanling cotton rats (14 days old) were fed three isocaloric diets containing 4, 8, or 16% protein for 24 days. Splenocyte subpopulations were assigned to one of eight categories by dual-staining with a panel of surface markers for T-cells (peanut agglutinin, PNA; soybean agglutinin, SEA, and Helix pomatia agglutinin, HP) and B-cells (rabbit-anti-rat immunoglobulin-G, BS). Total numbers of all splenocyte subpopulations were lower in rats subjected to moderate (8%) or severe (4%) protein restriction; B-cells were more sensitive to protein restriction than were T-cells. Prevalence (percent of total splenocytes) of PNA(-)/BS+ splenocytes was reduced, whereas prevalence of PNA(+)/BS- and SBA(-)/HP+ splenocytes was elevated with decreased protein intake. Multivariate statistical analysis of immune parameters revealed peripheral blood lymphocytes and splenocyte subpopulations as well as hemolytic complement activity and mean corpuscular volume most accurately described the degree of protein restriction and suggested a change in immunocompetence as a result of either moderate or severe protein restriction.