Abstract
Purpose:
Little is known about the susceptibility of posterior segment tissues, particularly the human retinal pigment epithelium (hRPE), to bacterial infections. The purpose of the study was to investigate the possibility of infecting the hRPE with Chlamydia trachomatis (CT), and to examine both the tropism of the pathogen for hRPE cells and expression of collagen and growth factors in response to the infection.
Methods:
Cultured hRPE and McCoy cells were inoculated with five CT clinical isolates (serovars D-K). To detect CT, samples were stained immunohistochemically with anti-MOMP antibodies at 24h, 48h, and 72h postinoculation (PI). The samples inoculated with the clinical isolate that had exhibited the highest infectivity were examined immunohistochemically for changes in the expression of collagen IV, collagen I, basic fibroblast growth factor (bFGF) and transforming growth factor β (TGF-β) of hRPE cells. Statistical significance was determined by a one-way ANOVA-test with Bonferroni post hoc test.
Results:
All clinical isolates showed a higher infectivity for hRPE cell culture than for McCoy cell culture. At 24 h PI, the percentage of cells with inclusions varied from 1.5±0.5% to 14.6±3.3% in hRPE cell culture against 0.4±0.1 to 8.9±0.2% in McCoy cell culture (P<0.05). In each phase of CT life cycle, the percentage of cells with inclusions in the hRPE culture was larger than that in the McCoy culture. The number of intracellular inclusions in both culture types decreased progressively from 24 h to 72 h postinoculation, with the cycle completed by the release of elementary bodies. Collagen IV, collagen I, bFGF and TGF-β expression at 48 h PI were significantly increased, by 1.3-, 2.1-, 1.5-, and 1.5-fold, respectively, in the CT-infected compared with control hRPE cell culture specimens (P<0.05).
Conclusions:
This study, for the first time, proved the possibility of infecting hRPE cultured cells with CT, which leads to proproliferative and proinflammatory changes in the expression of signaling molecules and extracellular matrix components. Furthermore, we demonstrated (1) increased susceptibility of RPE cells to CT infection, and (2) variability in infectivity among different clinical CT isolates. These results may be of importance in studying the vitreoretinal pathology.