Primary cultures of female swine genital epithelial cells in vitro: a new approach for the study of hormonal modulation of Chlamydia infection.

It is well recognized that genital Chlamydia trachomatis serovars D to K are responsible for epidemic sexually transmitted diseases and sequelae in the United States and worldwide. The chronic nature of these diseases is due, in part, to the fact that C. trachomatis is an obligate intracellular bacterial pathogen; this characteristic requires mammalian cell culture as well as animal models for the study of its infectious process in columnar epithelial cells of the genital tract of the target host. The majority of stock culture collection and expansion work with human chlamydial isolates has been performed with McCoy cells (fibroblast-like cells), which C. trachomatis does not infect in vivo (21). HeLa cells (epithelial cells from a cervical adenocarcinoma) have been used for most experimental analyses and are highly sensitive to chlamydial infection, but they are less representative of primary, differentiated target epithelial cells (4). As an alternative to the established transformed cell lines, a few studies have been performed with primary, hormone-responsive polarized human endometrial epithelial cells derived from women undergoing a hysterectomy for benign disease (17, 19, 29, 30). Important information about chlamydial attachment and infection which differed, in several aspects, from data obtained from non-hormone-responsive, nonpolarized, chlamydia-infected HeLa cells was obtained: (i) chlamydial inclusion development in primary human cervical and endometrial epithelial cells was patchy and uneven in distribution; (ii) levels of chlamydial attachment to and infectivity of primary human endometrial epithelial cells were significantly greater in estrogen-dominant than in progesterone-dominant cells; (iii) entry of infectious elementary bodies (EBs) into polarized, hormone-responsive, primary human endometrial epithelial cells was mediated predominately by clathrin-coated pit receptor-mediated endocytosis; and (iv) exit of chlamydiae from primary polarized human epithelial cells was pathogenesis directed, i.e., human noninvasive C. trachomatis serovar E progeny exited via the apical surface, whereas invasive C. trachomatis lymphogranuloma venereum-causing progeny were released at the basal domain. More recently, Davis et al. (8) have reported that a component associated with the estrogen receptor complex is associated with C. trachomatis serovar E EBs attached to the apical membrane surface of the polarized human endometrial epithelial cell line HEC-1B. As a substitute for human tissue, which is of limited availability for research purposes, different animal models have been used to evaluate Chlamydia-host cell interactions; these studies have included mice, guinea pigs, rats, and rabbits. The rat-C. trachomatis mouse pneumonitis model was used for examination of cell-cell interactions to determine the secretion of cytokines as well as the effects of hormones on the immune response and infectivity (13, 14, 20). While the evaluation of normality and sensitivity to hormone supplementation was the main goal achieved by these in vitro and in vivo models, the data from the rat model were essentially opposite to the results from human chlamydial infection data. Once the technique of nested PCR for genus-specific amplification of the Chlamydia omp-1 locus was established, it revealed a large separation between most of the animal and human chlamydial strains. However, new data derived from the 16S-23S ribosomal intergenic spacer signature sequence for the chlamydial groups determined that swine isolates of Chlamydia suis (or swine C. trachomatis-like strains) are highly related to the human C. trachomatis species (99% confidence). Further, the swine C. suis S-45 isolate is virtually identical to human genital C. trachomatis serovar D (100% confidence) (9, 10). Clinically, chlamydial diseases in swine include conjunctivitis, pneumonia, pericarditis, polyarteritis, and reproductive disorders. In the last named, Chlamydia has been reported to cause abortion in swine and to increase prenatal mortality (1, 26). In young piglets, chlamydiae produce a disease syndrome that is similar to that seen in infants following infection at the time of birth (2). Since the organ physiology of swine is very similar to that of humans, swine have become the favored model for dermatologists, gastroenterologists, and obstetricians. In addition, polarized porcine epithelial cell model systems have been developed for in vitro analysis of pregnancy paradigms, actions of hormones, prostaglandin secretion, and epithelial cell-stromal cell interactions (5, 6, 24, 32). This study evaluates the potential for using the C. suis S-45 swine primary genital tract epithelial cell culture model to follow up on previous data obtained from primary human endometrial epithelial cells (17, 19, 30), especially to study the influence of hormones on chlamydial attachment, adhesion-receptor interactions, and entry and development in genital tract cells, as well as microbicidal efficacy.