Chlamydia muridarum infection causes bronchointerstitial pneumonia in NOD.Cg-Prkdc^scidIl2rg^tm1Wjl/SzJ (NSG) mice

Abstract

The murine bacterial pathogen Chlamydia muridarum (Cm) has been used to study human Chlamydia infections in various mouse models. CD4+ T-cells, natural killer cells, and interferon-gamma (IFN-γ)–mediated immunity are important to control experimentally induced Cm infections. Despite its experimental use, natural infection by Cm has not been documented in laboratory mice since the 1940s. In 2022, the authors reported the discovery of natural Cm infections in numerous academic institutional laboratory mouse colonies around the globe. To evaluate the impact of Cm infection in severely immunocompromised mice, 19 NOD.Cg- Prkdcscid Il2rgtm1Wjl/SzJ (NSG) mice were cohoused with Cm shedding, naturally infected immunocompetent mice and/or their soiled bedding for 4 weeks and subsequently euthanized. Clinical disease, characterized by lethargy, dyspnea, and weight loss, was observed in 11/19 NSG mice, and 16/18 NSG mice had neutrophilia. All mice exhibited multifocal to coalescing histiocytic and neutrophilic bronchointerstitial pneumonia (17/19) or bronchiolitis (2/19) with intraepithelial chlamydial inclusions (CIs). Immunofluorescence showed CIs were often associated with bronchiolar epithelium. CIs were frequently detected by immunohistochemistry in tracheal and bronchiolar epithelium (19/19), as well as throughout the small and large intestinal epithelium without lesions (19/19). In a subset of cases, Cm colonized the surface epithelium in the nasopharynx (16/19), nasal cavity (7/19), and middle ear canal (5/19). Endometritis and salpingitis with intraepithelial CI were identified in a single mouse. These findings demonstrate that Cm infection acquired through direct contact or soiled bedding causes significant pulmonary pathology and widespread intestinal colonization in NSG mice.

Examining Intercage Transmission ofChlamydia muridarum: Impact of Barrier Husbandry and Cage Sanitization

“…16 Given that Cm EBs are of a similar size of 0.2 to 0.3 μm, it is plausible that aerosol transmission can occur, however we did not see evidence of it in the current study. 14,19,27,35,37…”

“…16 Given that Cm EBs are of a similar size of 0.2 to 0.3 μm, it is plausible that aerosol transmission can occur, however we did not see evidence of it in the current study. 14,19,27,35,37 In this regard, Cm appears to differ significantly from C. bovis, a relatively common pathogen of immunodeficient mice. 4,6,8,26 In contrast to Cm, C. bovis can be transmitted between cages when following strict microisolator cage changing technique in a biological safety cabinet as it is easily aerosolized.…”

“…24,25,26,35 Given Cm’s ability to induce a robust immune response, cause pathology in immunocompromised mice and persistent infection in both immunocompromised and immunocompetent mice, Cm should be excluded from research mouse colonies. 24,25,26,35…”

“…26 Cm infection, through its presumptive fecal-oral route of transmission of its metabolically inactive extracellular infectious elementary bodies (EBs), has been shown to cause significant disease, including severe pneumonia, dyspnea, and mortality, in highly immunodeficient and less severe pulmonary and potentially renal lesions in genetically engineered mouse (GEM) strains with select immune system alterations. 24,25,26,35 Given Cm's ability to induce a robust immune response, cause pathology in immunocompromised mice and persistent infection in both immunocompromised and immunocompetent mice, Cm should be excluded from research mouse colonies. 24,25,26,35 Cm is also highly prevalent within our program where 62.9% of the mouse holding rooms house Cm infected mice.…”

“…24,25,26,35 Given Cm's ability to induce a robust immune response, cause pathology in immunocompromised mice and persistent infection in both immunocompromised and immunocompetent mice, Cm should be excluded from research mouse colonies. 24,25,26,35 Cm is also highly prevalent within our program where 62.9% of the mouse holding rooms house Cm infected mice. 26 Its notable inter and intrainstitutional prevalence begs the question as to how the bacterium, which had not been detected in laboratory mice for almost a century, went undetected and became so widespread.…”