Interaction between turkey monocytes and avian Chlamydia psittaci in the presence of Mycoplasma sp.: the importance of nitric oxide

The interaction between Chlamydia psittaci and turkey monocytes was studied in vitro. Purified monocytes were inoculated with C. psittaci, in the pres ence or absence of Mycoplasma hyorhinis. Whereas turkey monocytes produced high amounts of nitric oxide (NO) following the inoculation with M. hyorhin is, inoculation with C. psittaci did not induce NO production in these phag ocytes. The monocytes strongly supported chlamydial growth, as demonstrated by the presence of inclusion forming units, the positive direct immunofluo rescence staining and transmission electron microscopy. In contrast, upon c o-inoculation of the monocytes with C. psittaci and M, hyorhinis, a reduced replication rate of C. psittaci was observed. N-G-monomethyl-L-Arginine, a competitive inhibitor for the enzyme NO-synthase, inhibited the NO product ion and reversed the antichlamydial activity of the M. hyorhinis co-inocula ted turkey monocytes. These results imply two considerations. First, as chl amydiae are obligate intracellular bacteria, special care should be taken t o guard chlamydial cultures from mycoplasmal contamination, in order to pre vent false results when investigating the response of immunomodulating cell s to chlamydial infection. Secondly, as a mycoplasmal co-infection in vitro has the capacity of inducing antichlamydial activity in turkey monocytes, through the action of NO, it could be suggested that a similar interaction might take place in vivo. Moreover, it was shown that avian M. gallisepticu m strains were also able to induce NO in turkey monocytes. Considering the high prevalence of both C. psittaci and Mycoplasma sp. in turkeys, this int eraction, through the pivotal role of NO, might influence the outcome of re spiratory diseases in turkeys. (C) 2000 Elsevier Science Ltd. All rights re served.