Local host response to chlamydial urethral infection in male guinea pigs

Abstract

Very little is known about the host response to chlamydial genital infection in the male, particularly about the nature of the local response in the urethra. In this study, the pathological and immunologic responses to urethral infection of the male guinea pig with Chlamydia caviae (Chlamydophila caviae) were characterized both during a primary infection and following a challenge infection. A dose-response experiment found that the 50% infectious dose for male urethral infection was 78 inclusion-forming units. The histopathologic response was similar to that of the female, with an initial acute inflammatory response followed by a chronic inflammatory response and plasma cell infiltration. Production of IgG and IgA antibodies in local urethral secretions developed following infection, and levels of both increased in a typical anamnestic response following a challenge infection. CD4 and CD8 T cells, as well as B cells, were observed in the local site by flow cytometry, with a slightly increased number of CD8 cells. Following challenge infection, the dominant anamnestic response was solely in the B-cell compartment, with only a minimal number of T cells. The T-cell response was clearly a Th1 response, as judged by increased levels of gamma interferon (IFN-gamma), interleukin-12 p40 (IL-12p40), and IL-2. The proinflammatory cytokines and chemokines IL-8, IL-1beta, tumor necrosis factor alpha (TNF-alpha), CCL2 (monocyte chemoattractant protein 1 [MCP-1]), and CCL5 (RANTES) were elicited in the urethra following primary infection, but only CCL5 showed increased levels upon challenge. This study represents the first comprehensive analysis of the local immune response in the male urethra to a chlamydial genital infection.

FIG. 1.

Kinetics of urethral infection in male guinea pigs following inoculation with different doses of chlamydiae. Each data point represents the mean number of IFU for animals that became infected. To the right of each dose in the key, the ratio of the number of animals that became infected to the total number of animals inoculated with that dose is given in parentheses. The infection courses of animals infected with 10¹, 10², and 10³ IFU were significantly different from those of animals inoculated with 10⁴ IFU.

FIG. 2.

Pathological responses to chlamydial urethral infection at various times after infection. (Left) Distal area; (center) proximal area; (right) higher-magnification image of the boxed section of the corresponding distal or proximal area.

FIG. 3.

Mean pathology scores of tissues for the indicated parameters at various times after infection. Each error bar represents 1 standard deviation. Tissues from 3 to 5 guinea pigs were evaluated at each time point.

FIG. 4.

Immunohistochemical staining of chlamydial inclusions in urethral tissue. Shown are the distal urethra (A) and the proximal urethra (B) on day 4 after infection. Arrows indicate chlamydial inclusions.

FIG. 5.

Mean antibody responses to the GPIC agemt in sera and secretions following primary and challenge infections. Error bars represent 1 standard deviation. Serum samples were collected sequentially from 10 guinea pigs. All urethral secretion samples from the 10 animals were pooled for the determination of antibody titers.

FIG. 6.

Proliferation responses of iliac lymph node and splenic cells to chlamydial antigen. Each bar represents the mean stimulation index for 6 animals, and each error bar represents 1 standard deviation. Asterisks indicate that the difference between the response in the iliac lymph node and the response in the spleen was significant (P < 0.001).

FIG. 7.

Kinetics of the cellular response in the urethra following primary and challenge infections as assessed by flow cytometry. Each data point represents the mean and standard deviation for 5 animals. The number of CD8 cells on day 14 was significantly greater than the number of CD4 cells (P = 0.008). The number of B cells following challenge infection was significantly greater than the numbers of CD4 and CD8 T cells on each of the days following challenge (P, <0.01 to 0.001).

FIG. 8.

Kinetics of 16S RNA transcripts of the GPIC agent following a primary and a challenge urethral infection. Each symbol represents a single animal, and the line represents the mean of the responses of 5 animals at each time point. Filled symbols indicate that the animal was positive for chlamydiae by determination of 16S RNA transcripts. Where the symbols overlap, the total number positive for 16S RNA is given over the total number of animals at each time.

FIG. 9.

Kinetics of chemokine and cytokine response following a primary and a challenge urethral infection. Each symbol represents a single animal, and each line represents the mean of the responses of 5 guinea pigs. Filled symbols indicate that the animal was positive for chlamydiae by determination of 16S RNA transcripts.

FIG. 10.

Kinetics of the T-cell cytokine response following a primary and a challenge urethral infection. Each symbol represents a single animal, and each line represents the mean of the responses of 5 animals. Filled symbols indicate that the animal was positive for chlamydiae by determination of 16S RNA transcripts.