Primed Mycobacterial Uveitis (PMU) as a Model for Post-Infectious Uveitis

Abstract

The term 'uveitis' describes a heterogeneous set of conditions that all feature intraocular inflammation. Broadly, uveitis is defined by etiology: infection or autoimmunity. Infectious uveitis requires treatment with the appropriate antimicrobial agents, while autoimmune uveitis requires treatment with corticosteroids or other immunosuppressive agents. Post-infectious uveitis is a form of chronic uveitis that requires corticosteroids to control immune sequela following the initial infection. Uveitis associated with Mycobacterium tuberculosis (Mtb) infection is a well-recognized form of post-infectious uveitis, but the mechanisms of disease are not fully understood.To understand the role mycobacterial antigens and innate ligands play in stimulating chronic ocular inflammation following mTB infection, the model Primed Mycobacterial Uveitis (PMU) was developed for use in mice. This manuscript outlines the methods for generating PMU and monitoring the clinical course of inflammation using color fundus and optical coherence tomography (OCT) imaging. PMU is induced by immunization with heat-killed mycobacterial extract followed by intravitreal injection of the same extract into one eye seven days later. Ocular inflammation is monitored longitudinally using in vivo imaging and followed by sample collection for a wide range of assays, including histology, flow cytometry, cytokine analysis, qPCR, or mRNA sequencing.The mouse model of PMU is a useful new tool for studying the ocular responses to mTB, the mechanism of chronic uveitis, and for preclinical effectiveness tests of new anti-inflammatory therapies.

Systemic prime exacerbates the ocular immune response to heat-killed Mycobacterium tuberculosis

“…Mice were maintained with standard chow and medicated water (acetaminophen 300 mg/kg) ad libitum, with 12 h light: 12 h dark cage lighting under specific pathogen-free conditions. PMU induction in mice is a modification of a protocol previously published in rabbits ( Mruthyunjaya et al, 2006 ; Cousins, 1992 ; Jaffe et al, 1998 ) and rats( K. L. Pepple et al, 2015 ; Kathryn L. Pepple, Wilson, and Van Gelder, 2018 ) and has been reported previously ( Gutowski et al, 2017 ; John et al, 2020 , 2021 ). Briefly, on day -7 animals receive a subcutaneous injection of 100 μg killed mycobacterium tuberculosis H37Ra antigen (#231141, Difco Laboratories, Detroit, MI) in a 0.1 cc emulsion of incomplete Freund’s adjuvant (#263910, Difco Laboratories, Detroit, MI) divided with half the dose to each hip.…”

“…Close attention to corneal protection during OCT imaging and post-anesthesia recovery is important to prevent corneal damage and poor image quality. For recommendations on corneal protection considerations during OCT imaging see ( John et al, 2021 ).…”

“…To model systemic infection preceding ocular exposure to Mtb, HKMtb is first administered by subcutaneous route seven days prior to intravitreal injection of a small amount (5 μg) of HKMtb. This approach to Mtb associated uveitis induction is termed primed mycobacterial uveitis (PMU) ( John et al, 2021 ). PMU generates an acute panuveitis that slowly resolves into a chronic posterior uveitis over the following month.…”