Tuesday, July 3, 2007

Immune function of Vitamin C

There is a large body of evidence that vitamin C plays
an important role in the biochemistry of the human
immune system, particularly in the stimulation of
phagocytosis. Leucocytes accumulate ascorbic acid
after uptake from the plasma by active transport
(Moser, 1987), suggesting an involvement of the vitamin
in the normal function of these cells. The concentration
of ascorbate in monocytes, for example, is over
80 times higher than that in plasma (Evans et al., 1982)
and macrophages contain about twice as much ascorbate
as neutrophils and monocytes (Schmidt & Moser,
1985). Vitamin C accumulation in activated human
neutrophils is increased as much as ten-fold above the
concentrations present in resting neutrophils as a result
of a novel vitamin recycling mechanism. Extracellular
ascorbate is oxidized to dehydroascorbic acid by
oxidants generated by the activated neutrophil. The
dehydroascorbic acid is preferentially taken up by the
neutrophil and reduced intracellularly to ascorbate
within minutes (Washko et al., 1993). Ascorbate, as an
antioxidant, protects phagocytes from self-destruction
by reactive oxidants (Muggli, 1993). It also neutralizes
reactive oxidants released extracellularly by
activated phagocytes, thereby preventing damage to
surrounding host tissue (Anderson & Lukey, 1987).

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