In this study, we have provided a quantitative assessment of the T-cell, B-cell, and Mac-1-expressing-cell responses in different sections of the guinea pig genital tract following intravaginal infection or reinfection with the agent of GPIC. Previously, we had described the pathologic response to the infection in similar groups of animals by histopathology (16
). In those studies, we reported that in the primary infection, an acute and chronic inflammatory response was noted in each of the infected tissues. Initially the heaviest response was in the exo- and endocervix, but after about 7 days, pathologic changes could be seen in the endometrium and the oviducts as well. However, while organisms could be demonstrated in the endometrium and oviducts of 80% of the animals, only 45% of the animals had detectable pathology. In the current study, we also noted that the strongest reaction was in the lower genital tract with a marked influx of Mac-1-bearing cells and T cells. B cells remained relatively low in each of the tissues throughout the course of the infection. The Mac-1 response is most likely indicative of the inflammatory response in general, since this marker can be found on PMNs, monocytes, and macrophages.
Particularly in animals infected with 107
IFU of the GPIC agent, there was a much greater response of Mac-1-bearing cells in all parts of the genital tract, which closely paralleled the histopathology data previously published (16
). Also, it was interesting that there was a dose response with regard to the Mac-1 response. Infection with 107
IFU yielded a higher number of cells than did infection with 106
IFU. These data are supported by observations that we have made of the TNF-α response following GPIC genital infection. In that study, the level of TNF-α detected in genital secretions was positively correlated with the number of chlamydiae in the inoculum. Thus, these data would suggest that the production of proinflammatory cytokines responsible for the acute inflammatory response might be dependent on the number of organisms present. It has been demonstrated by others that infection of macrophages with chlamydiae can elicit TNF-α production either via lipopolysaccharide (LPS) stimulation of the cells or possibly even through heat shock protein 60 (hsp60) stimulation of the cells (1
). Moreover, Rasmussen et al. (18
) have shown that chlamydial infection of epithelial cells can also elicit interleukin 1 (IL-1) and IL-8 production, both of which are actively involved in the acute inflammatory response. In contrast to the Mac-1 response, there was no obvious dose dependency upon the T-cell or B-cell influx.
While the T-cell response is also supportive of our earlier histopathologic observations, it was surprising that the numbers of CD4 and CD8 cells were equivalent. This is in contrast to the MoPn mouse genital tract model, in which the dominant T-cell phenotype in the genital tract following infection is CD4, while CD8 T cells are generally present in lower numbers (3
). Nevertheless, this ratio of CD4 to CD8 cells in the guinea pig approximates more closely what has been observed in the endocervix of humans infected with C. trachomatis
) and nonhuman primates infected with C. trachomatis
in the genital tract (21
) or in the conjunctiva (24
). We have also noted equivalent numbers of CD4 and CD8 cells in the guinea pig conjunctiva upon ocular infection with GPIC (R. G. Rank, unpublished data). In the murine model, CD8 cells have been shown to have a protective role, but they are not essential for resolution of the infection, nor have they been positively associated with pathology. The demonstration of a major CD8 response in the guinea pig genital tract following chlamydial infection would suggest that CD8 cells play a significant role in either protection or the production of pathology or both. Thus, as in many other parameters, the guinea pig model continues to reflect very closely what is seen in the human and nonhuman primates and can provide a convenient method for evaluating the role of this cell population in chlamydial disease.
Perhaps the most important observation in this study is the demonstration of an increased T-cell response in the oviducts upon reinfection in the genital tract. When compared to the number of T cells present in the oviduct 21 days after a primary infection, there was a significant increase in both CD4 and CD8 T cells in the oviduct 21 days after reinoculation. It was also of interest that the number of B cells was significantly increased upon reinfection. In contrast, the number of Mac-1-expressing cells in the tissues after reinfection was no different than during the primary infection. These data are all consistent with a specific pathologic cell-mediated immune reaction that has been proposed by ourselves and others to explain the more severe pathology seen upon reinfection in different animal models (17
). Since the level of immunity to reinfection in the guinea pig is such that there is only a low level of infection upon reinoculation (13
), the presence of an enhanced response in the oviducts suggests that very little antigen is required to elicit the response.
An unexpected result was the finding that the enhanced T- and B-cell responses 21 days after reinfection were limited to the oviduct and were not apparent in the lower genital tract or the endometrium. In fact, the T-cell response was lower at day 10 after reinoculation when compared to T cells at day 10 after the primary infection. This was most likely the result of a markedly reduced infection and clearance of the organisms by the serum and secretion antibody (12
). It may also indicate that there are tissue differences that facilitate T-cell homing. Kelly et al. (3
) recently reported that vascular cell adhesion molecule 1 (VCAM-1) and mucosal addressin cell adhesion molecule 1 (MAdCAM-1) persist longer in the upper genital tract of the mouse compared to their survival in the cervix and endometrium so that there is differential homing to the upper tract. The implications for human disease are obvious. There is evidence that there is a much greater risk of tubal obstruction in patients with repeated infection (23
). The data presented here and in the mouse model (3
) support the concept that fallopian tube tissue may actually facilitate enhanced disease through prolonged expression of addressins and increased homing of T cells to the site.
This study also establishes this model as an ideal tool to quantitatively examine the protective effect of a vaccine candidate on the pathologic response or the possibility that the vaccine might actually elicit a more severe pathologic response, particularly after multiple challenges. The guinea pig model has shown a remarkable resemblance to the human disease, and, coupled with the ability to demonstrate sexual transmission of chlamydial infection, it presents a unique opportunity to evaluate potential vaccine candidates.