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* 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
CD3intermediate/NKR-P1+). Based on regression
analysis of flow cytometry data, the phenotype of most NKT cells was
CD3intermediate/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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