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-cell relative to the B-cell pool.

We report cell numbers within major subsets of lymphocytes in the spleen, mesenteric nodes, and recirculating pool of weanling 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 of the 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 of T 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 CD4(+)-CD8+ ratio and that PEM induces greater involution within the T-cell system than within the B-cell system.