Depression of thymus-dependent immunity in wasting protein-energy malnutrition does not depend on an altered ratio of helper (CD4 ) to suppressor (CD8 ) T cells or on a disproportionately large atrophy of the T-celI relative to the B-cell poo113

ABSTRACF We report cell numbers within major subsets oflymphocytes in the spleen, mesenteric nodes, and recirculating pool ofweanling mice subjected to protein-energy malnutrition (PEM). PEM and thymus (T)-dependent immunodepression were induced in male C57BL/6J mice by a low-protein (LP) diet fed ad libitum. Recirculating lymphocyte numbers were estimated by enumerating labeled and unlabeled cells after equilibration of a known number of fluorescein isothiocyanate-labeled C57BL/6J donor lymphocytes within well-nourished or LP recipients. Involution of the recirculating lymphocyte pool of the LP group was proportionately less than the lymphoid atrophy ofthe spleen and mesenteric nodes. The LP protocol exerted no influence on the ratio of helper (CD4 ) to suppressor (CD8 ) T cells and increased the ratio ofT cells to B cells in the secondary lymphoid organs and recirculating pool. These results challenge two established concepts: that T-dependent immunodepression in PEM depends on a reduced CD4tCD8 ratio and that PEM induces greater involution within the T-cell system than within the B-cell system. Am J C/in Nutr 199 1 ;53: 1329-35.