The common parasite Toxoplasma gondii induces prostatic inflammation and microglandular hyperplasia in a mouse model

Abstract

Background: Inflammation is the most prevalent and widespread histological finding in the human prostate, and associates with the development and progression of benign prostatic hyperplasia and prostate cancer. Several factors have been hypothesized to cause inflammation, yet the role each may play in the etiology of prostatic inflammation remains unclear. This study examined the possibility that the common protozoan parasite Toxoplasma gondii induces prostatic inflammation and reactive hyperplasia in a mouse model.

Methods: Male mice were infected systemically with T. gondii parasites and prostatic inflammation was scored based on severity and focality of infiltrating leukocytes and epithelial hyperplasia. We characterized inflammatory cells with flow cytometry and the resulting epithelial proliferation with bromodeoxyuridine (BrdU) incorporation.

Results: We found that T. gondii infects the mouse prostate within the first 14 days of infection and can establish parasite cysts that persist for at least 60 days. T. gondii infection induces a substantial and chronic inflammatory reaction in the mouse prostate characterized by monocytic and lymphocytic inflammatory infiltrate. T. gondii-induced inflammation results in reactive hyperplasia, involving basal and luminal epithelial proliferation, and the exhibition of proliferative inflammatory microglandular hyperplasia in inflamed mouse prostates.

Conclusions: This study identifies the common parasite T. gondii as a new trigger of prostatic inflammation, which we used to develop a novel mouse model of prostatic inflammation. This is the first report that T. gondii chronically encysts and induces chronic inflammation within the prostate of any species. Furthermore, T. gondii-induced prostatic inflammation persists and progresses without genetic manipulation in mice, offering a powerful new mouse model for the study of chronic prostatic inflammation and microglandular hyperplasia.

Keywords: Toxoplasma gondii; hyperplasia; inflammation; parasite; prostate.

FIGURE 1

T. gondii chronically encysts in the mouse prostate. Male CBA/J Mice were injected intraperitoneally with either sterile PBS or 40 000 PruΔhpt + ldhGFP T. gondii tachyzoites, and euthanized at either 14 (n = 14), 28 (n = 16), or 60 (n = 6) days post infection (DPI), and their brains and prostates were collected. (A) T. gondii localization and encystation in the mouse prostate was confirmed by detection of T. gondii-expressed GFP by Western blot analysis of protein extracts from either uninfected control mice (Con) or infected mice (Inf) at the time indicated. (B) T. gondii localization and chronic encystation in the mouse prostate was visualized by immunofluorescence in all infected mice prostates at 14, 28, and 60 DPI. Dorsal lateral prostate (DLP) sections from infected mice for the time indicated were co-stained for T. gondii-expressed GFP (green) and the T. gondii specific cyst wall marker Dolichols biflorus agglutinin (DBA) conjugated to rhodamine (red). Arrow heads denote T. gondii cysts; scale bars mark 25 µm. Serial section of the GFP/DBA stained slides, stained with hematoxylin and eosin (H&E). Arrow heads denote T. gondii cysts; scale bars mark 25 µm. (C) To confirm specificity of T. gondii labeling, 60 days prostates were co-stained with bradyzoite antigen (Bag1), the parasite specific heat shock protein, Hsp30 (green), and DBA (red) and are shown in an 80× image. Scale bars represent 25 µm

FIGURE 2

T. gondii infection induces acute and chronic inflammatory responses in the mouse prostate. (A) Representative 10× (left) and 40× (right) images of (H&E)-stained sections of dorsal lateral prostates (DLP) from uninfected control (left) and T. gondii infected (right) mice at 14, 28, and 60 DPI Scale bars mark 25 µm. (B) Inflammatory infiltrate scores from DLP, ventral (VP), and anterior lobes (AP) of age-matched control and T. gondii infected mice at 14, 28, and 60 DPI, (n = 6–10, each group) using the established scoring system published by Boehm et al. Data are presented as the mean inflammatory infiltrate score ± SEM and compared to uninfected control mice by two-tailed student’s t-test. *P < 0.05

FIGURE 3

Chronic T. gondii infection of the mouse prostate induces monocytic and lymphocytic infiltrate. (A) Representative immunofluorescent images of inflammatory infiltrate in the DLP of control (uninfected age-matched) and T. gondii-infected mice at 14 (n = 6), 28 (n = 10), and 60 (n = 5) DPI stained with the B-cell marker CD20 (top, green), the monocyte marker F4-80 (middle, red), and the T-cell marker CD3ε (bottom, red). Scale bars mark 25 µm. (B) Quantification of immune cells within the CD45+ population by flow cytometry. Data shown are the ratio of total inflammatory cells to total live cells (whole bar length), and the ratio to total live cells of CD3ε+ T lymphocytes (black portion of the bar), CD20+ B lymphocytes (grey portion), F4-80+ monocytes (hatched portion), and Cd11c+/CD8α+ dendritic cells (white portion) in T. gondii-infected and age-matched control mice at 28 DPI. Data are presented as mean ratio to total live cells ± SEM; infected and control groups were compared by two-tailed student’s t-test. *P < 0.05 (n = 6)

FIGURE 4

Prostatic inflammation induced by T. gondii results in reactive hyperplasia. (A) Representative 20× (left) and 40× (right) images of H&E-stained DLPs from uninfected control (left) and T. gondii-infected (right) mice at 14, 28, and 60 DPI. Scale bars mark 25 µm. (B) Hyperplasia scores from DLP, VP, and AP of age-matched-control and T. gondii-infected mice at 14, 28, and 60 DPI (n = 6–10, each group) using the scoring system established by Boehm et al. Data are presented as the mean hyperplasia score ± SEM. Infected mice are compared to uninfected control mice by two-tailed student’s t-test. *P < 0.05

FIGURE 5

T. gondii-induced reactive hyperplasia exhibits epithelial proliferation, expansion of transit amplifying cells, and proliferative microglandular hyperplasia in chronically infected prostates. Proliferation in T. gondii-infected and control mice was determined by BrdU-labeling 2 h prior to sacrifice followed by immunofluorescence. (A) Representative BrdU staining at 28 DPI. BrdU (green), pan-cytokeratin (red), scale bars indicate 25 µm. (B) Quantified data of BrdU-positive epithelial cells from infected and control prostates harvested at 14 (n = 6), 28 (n = 6), and 60 (n = 4) DPI. Three random 20× views/mouse prostate were quantified and averaged as percent proliferating (BrdU+) epithelial cells to total epithelial cells in the field of view. Data are presented as the mean % BrdU+ epithelial cells ± SEM in each group. Infected mice are compared to age-matched control by two-tailed student t-test; *P < 0.05. (C) Expansion of epithelial transit amplifying cells (TACs) determined by cytokeratin 5 and 8 co-immunofluorescent staining. Representative T. gondii-infected 28 and 60 days mouse prostates immunostained with the basal epithelial marker cytokeratin 5 (CK5) (red) and luminal epithelial marker cytokeratin 8 (CK8) (green), as indicated by arrow heads. Scale bars represent 25 µm

FIGURE 6

Chronic T. gondii infection elicits proliferative inflammatory reactive microglandular hyperplasia in the mouse prostate at 28 (top) and 60 DPI (bottom). This phenotype is observed in 13/16 prostates at 28 DPI and is fully penetrant at 60 DPI (n = 6)