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Infect. Immun., May 1995, 1870-1875, Vol 63, No. 5
JM Carlin and JB Weller
One mechanism by which interferons (IFNs) can inhibit chlamydial infection
is by the induction of the enzyme indoleamine 2,3-dioxygenase (IDO), which
restricts the availability of tryptophan, which is required for chlamydial
growth. Other immunomodulating agents, including interleukin-1 (IL-1), can
interact synergistically with IFNs, resulting in increased IDO activity in
macrophages. The objectives of this study were to establish that IL-1 can
enhance IFN-mediated inhibition of chlamydial growth by increasing the
amount of IDO activity induced by IFNs and to identify immunomodulatory
agents in culture supernatants from chlamydia-infected macrophages that
interact synergistically with IFNs in restricting chlamydial growth.
Monocyte- derived macrophages were treated with IL-1 combined with gamma
IFN (IFN- gamma) or IFN-beta. The ability of treated cells to support the
growth of Chlamydia psittaci was directly related to the amount of IDO
activity induced; as IDO activity increased, so did inhibition of
chlamydial growth. Furthermore, concentrations of IFNs were identified at
which little IDO activity was induced and chlamydial growth was permitted
yet which in the presence of IL-1 resulted in increased IDO activity and
restriction of chlamydial growth. The addition of exogenous tryptophan
reversed the effect of combined IFN and IL-1 treatment, indicating that IDO
activity induced by combined cytokine treatment was responsible for
chlamydial inhibition. Supernatants from chlamydia-infected macrophages
were capable of potentiating IDO induction by IFN-gamma and of restricting
the growth of C. psittaci. Antibody to IL-1 beta neutralized the
potentiating effects of supernatants from chlamydia-infected cells on both
IDO induction and chlamydial inhibition. Thus, IL-1 produced in response to
chlamydial infection may contribute to the elimination of the infection.
Copyright © 1995, American Society for Microbiology
Potentiation of interferon-mediated inhibition of Chlamydia infection by interleukin-1 in human macrophage cultures
Department of Microbiology, Miami University, Oxford, Ohio 45056, USA.
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