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Article

Chronic Marginal Vitamin A Status Affects the Distribution and Function of T Cells and Natural T Cells in Aging Lewis Rats¹

^* Graduate Program in Nutrition and Department of Nutrition, The Pennsylvania State University, University Park, PA 16802

²To whom correspondence should be addressed at Department of Nutrition, The Pennsylvania State University, 126-S Henderson Building, University Park, PA 16802-5400. Phone: (814) 865-4721; FAX: 814 865-4723

Although both vitamin A (VA) deficiency and aging are independently associated with alterations in immune function, the effects of marginal VA status or VA supplementation on the immune system during aging were not studied. A long-term dietary study was conducted in a rat model of aging to quantify changes in T-cell populations in blood and spleen, including T-cells bearing a marker of natural killer (NKT) cells. The study included nine treatment groups [three levels of dietary VA: marginal (0.35 RE/kg diet), control (4.0 RE/kg diet), and supplemented (50 RE/kg diet); and three age groups: young (2–3 mo), middle-aged (8–10 mo), and old 20–22 mo); diets were fed continuously from weaning to the end of the study period. CD3⁺/CD4⁺ T-cells decreased in percentage and number in blood with age, CD8⁺ cells increased (%), and the CD4/CD8 ratio decreased. Conversely, aging was associated with increased NKT cells (phenotype CD3^intermediate/NKR-P1⁺). Based on regression analysis of flow cytometry data, the phenotype of most NKT cells was CD3^intermediate/NKR-P1⁺/CD28^-. NKT cells, which are most likely of extrathymic origin, accounted for most of the decrease in the CD4/CD8 ratio. Marginal VA status, particularly in older rats, was associated with increases in the percentage of CD8⁺ T cells, percentage and number of NKT cells, and peripheral blood cell anti-CD3-stimulated proliferative response, and decreases in the CD4/CD8 T-cell ratio and splenic cell interleukin-2 production. These differences and the reciprocal changes observed for NKT cells vs. T- and classical NK cells in aging VA-marginal rats suggest that low VA status during aging may increase the risk of infectious or neoplastic diseases that require a normal balance of T-cell or NK-cell responses.

KEY WORDS: • T-cells • natural T-cell • immunocompetence • vitamin A supplementation • rats

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