Characterization and comparison of differentially expressed genes involved in Chlamydia psittaci persistent infection in vitro and in vivo.

Chlamydia psittaci is an obligate intracellular zoonotic pathogen that can enter a persistence state in host cells. While the exact pathogenesis is not well understood, this persistence state may play an important role in chronic Chlamydia disease. Here, we assess the effects of chlamydial persistence state in vitro and in vivo by transmission electron microscopy (TEM) and cDNA microarray assays. First, IFN-γ-induced C. psittaci persistence in HeLa cells resulted in the upregulation of 68 genes. These genes are involved in protein translation, carbohydrate metabolism, nucleotide metabolism, lipid metabolism and general stress. However, 109 genes were downregulated following persistent C. psittaci infection, many of which are involved in the TCA cycle, expression regulation and transcription, protein secretion, proteolysis and transport, membrane protein, presumed virulence factor, cell division and late expression. To further study differential gene expression of C. psittaci persistence in vivo, we established an experimentally tractable mouse model of C. psittaci persistence. The C. psittaci-infected mice were gavaged with either water or amoxicillin (amox), and the results indicated that the 20 mg/kg amox-exposed C. psittaci were viable but not infectious. Differentially expressed genes (DEGs) screened by cDNA microarray were detected, and interestingly, the results showed upregulation of three genes (euo, ahpC, prmC) and downregulation of five genes (pbp3, sucB_1, oppA_4, pmpH, ligA) in 20 mg/kg amox-exposed C. psittaci, which suggests that antibiotic treatment in vivo can induce chlamydial persistence state and lead to differential gene expression. However, the discrepancy on inducers between the two models requires more research to supplement. The results may help researchers better understand survival advantages during persistent infection and mechanisms influencing C. psittaci pathogenesis or evasion of the adaptive immune response.

Intracerebral infection of mice with ovine strains of Chlamydia psittaci: an animal screening test for the assay of vaccines.

Intracerebral inoculation of mice with the A22 strain of ovine C. psittaci gave a reproducible non-lethal infection; multiplication of the inoculum could be quantitated by titration of mouse brain extracts in tissue culture. Mice which had recovered from infection, or which had been inoculated subcutaneously with living organisms of A22 strain, showed solid resistance to intracerebral challenge infection. However, subcutaneous inoculation of formalin-inactivated chlamydia showed little protective effect unless given in very high dosage. Inactivated vaccines of the heterologous ZC113 strain gave better, but still incomplete, protection against A22 challenge infection than did the homologous inactivated vaccine. The implication of these findings is discussed. The mouse intracerebral protection test appears to be a suitable laboratory procedure for assessing the potency of vaccines against enzootic ewe abortion and for comparing the immunological cross-protection between the various strains of C. psittaci currently found in the natural disease in sheep.

Lymphokine-mediated microbistatic mechanisms restrict Chlamydia psittaci growth in macrophages.

The obligate intracellular procaryote Chlamydia psittaci replicated in cultures of macrophages taken from the peritoneal cavities of unstimulated or thioglycollate-elicited A/J mice. When treated with supernatant fluids (lymphokines) from C. psittaci-immune mice spleen cells that were stimulated for 24 hr in vitro by the mitogen concanavalin A, resident macrophages supplemented with heart infusion broth (8 mg/ml) and elicited macrophages markedly suppressed intracellular chlamydial development. Uptake of the parasites was unaffected by LK-activated macrophages. The LK-induced inhibition was a static rather than a cidal effect. Chlamydial replication was detected 24 to 41 hr after removal of LK and infection with C. psittaci. Evidence that intermediates of oxygen metabolism did not contribute to the microbistatic process in either resident or elicited macrophages was provided by the inability of exogenous catalase, deprivation of glucose, or pretreatment with phorbol myristate acetate (PMA) to reverse LK-induced inhibition of parasite replication.