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

Populations of cotton rats (Sigmodon hispidus) frequently exhibit extr eme fluctuations in abundance, which have been attributed to changes i n food quality and its possible effect on survival of juveniles. Weanl ing 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 dete rmined the influences of onset of protein restriction at an earlier ag e compared with previous studies. Weanling cotton rats (14 days old) w ere fed three isocaloric diets containing 4, 8, or 16% protein for 24 days. Splenocyte subpopulations were assigned to one of eight categori es by dual-staining with a panel of surface markers for T-cells (peanu t agglutinin, PNA; soybean agglutinin, SEA, and Helix pomatia agglutin in, HP) and B-cells (rabbit-anti-rat immunoglobulin-G, BS). Total numb ers of all splenocyte subpopulations were lower in rats subjected to m oderate (8%) or severe (4%) protein restriction; B-cells were more sen sitive to protein restriction than were T-cells. Prevalence (percent o f total splenocytes) of PNA(-)/BS+ splenocytes was reduced, whereas pr evalence of PNA(+)/BS- and SBA(-)/HP+ splenocytes was elevated with de creased protein intake. Multivariate statistical analysis of immune pa rameters revealed peripheral blood lymphocytes and splenocyte subpopul ations as well as hemolytic complement activity and mean corpuscular v olume most accurately described the degree of protein restriction and suggested a change in immunocompetence as a result of either moderate or severe protein restriction.