Vitamin A deficiency impairs cytotoxic T lymphocyte activity in Newcastle disease virus-infected chickens.

The effect of vitamin A deficiency on cytotoxic T lymphocyte (CTL) activity was investigated during the acute phase of disease 7 days after primary inoculation and 1 day after secondary inoculation in chickens with or without Newcastle disease virus (NDV, La Sota strain) infection. Day-old chickens with limited vitamin A reserves were fed purified diets containing either marginal (ad libitum) or adequate (pair-fed) levels of vitamin A, and at 3 weeks of age half of the chickens in each group were infected with NDV. Cytotoxic activity was investigated during the acute phase of disease (7 days after primary inoculation) and 1 day after secondary inoculation, in an assay system with either peripheral blood lymphocytes (PBL) or nonadherent splenocytes as effector cells and adherent splenocytes from the same animal as target cells. After primary inoculation, cytotoxic activity could only be demonstrated in nonadherent splenocytes. Vitamin A deficiency resulted in significantly reduced CTL activity at all effector/target cell ratios tested. After reinfection CTL activity could also be demonstrated in PBL, but only from chickens fed the control diet, suggesting a diminished pool of CTL in vitamin A deficiency. The results of this study indicate that vitamin A deficiency impairs CTL activity - a part of the cell-mediated defense system - and this may have important implications for recovery from viral infection.