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Department of International Health, School of Public Health, University of Alabama at Birmingham, Birmingham, AL 35294 and * Department of Microbiology, University of Alabama at Birmingham, Birmingham, AL 35294
3To whom correspondence should be addressed at USDA Western Human Nutrition Research Center and Department of Nutrition, University of California, Davis, CA 95616.
Vitamin A supplementation during acute pneumonia has not improved
recovery in most human clinical trials. We hypothesize that high
vitamin A intake may decrease the production of T-helper type-1
(Th1) cytokines and thereby inhibit antiviral responses. Such decreases
might impair recovery from viral respiratory infections. We thus
examined the effect of three interventions on viral pneumonia:
1) a high level vitamin A [250,000 IU/kg
diet or 75,000 retinol equivalents (RE)/kg], or 2)
control diet (4000 IU/kg diet or 1200 RE/kg) given before
and during infection, and 3) initiating the high level
diet upon infection to simulate the adjuvant therapy used in clinical
trials. No difference was seen among the interventions in severity of
disease (weight loss, lung virus titers and survival). However, both
the high level diet group and the group in which vitamin A was
increased at the time of infection had greater salivary immunoglobulin
(Ig)A responses (geometric means, 166 and 105 µg/L,
respectively) than did the control group (59 µg/L)
(P = 0.0019). In contrast, the serum IgG response
was higher in the control group (324 ± 158 mg/L) than in the high
level group (225 ± 95 mg/L) (P = 0.028),
although it did not differ from the group in which the diet was changed
upon infection (230 ± 163 mg/L) (P = 0.084).
The production of interferon-
(IFN-
), a Th1 cytokine, was lower
in the high level diet group (median, 0.153 µg/L)
compared with the control group (median, 0.839 µg/L)
(P = 0.014), whereas the production of
interleukin-10 (IL-10), a Th2 cytokine, was higher with the high level
diet (median, 0.304 µg/L) than with the control
(median, 0.126 µg/L) (P = 0.022).
This change in the Th1/Th2 pattern was not sufficient to affect
recovery from viral pneumonia but may account for the increased IgA and
decreased IgG responses seen with high level dietary vitamin A in this
study. These data reinforce the lack of utility of vitamin A in
treating acute pneumonia in children and suggest that high dose vitamin
A supplements may enhance Th2-mediated immune responses, which are
particularly beneficial in the case of extracellular bacterial and
parasitic infections and IgA-mediated responses to mucosal
infections.
KEY WORDS: vitamin A pneumonia influenza A virus Mus musculus immunoglobulin A interleukin-10 interferon-
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