The immune response in tubercular uveitis and its implications for treatment: From anti-tubercular treatment to host-directed therapies

Tubercular uveitis (TB-uveitis) remains a conundrum in the uveitis field, which is mainly related to the diverse clinical phenotypes of TB-uveitis. Moreover, it remains difficult to differentiate whether Mycobacterium tuberculosis (Mtb) is present in the ocular tissues, elicits a heightened immune response without Mtb invasion in ocular tissues, or even induces an anti-retinal autoimmune response. Gaps in the immuno-pathological knowledge of TB-uveitis likely delay timely diagnosis and appropriate management. In the last decade, the immunopathophysiology of TB-uveitis and its clinical management, including experts' consensus to treat or not to treat certain conditions with anti-tubercular treatment (ATT), have been extensively investigated. In the meantime, research on TB treatment, in general, is shifting more toward host-directed therapies (HDT). Given the complexities of the host-Mtb interaction, enhancement of the host immune response is expected to boost the effectiveness of ATT and help overcome the rising burden of drug-resistant Mtb strains in the population. This review will summarize the current knowledge on the immunopathophysiology of TB-uveitis and recent advances in treatment modalities and outcomes of TB-uveitis, capturing results gathered from high- and low-burden TB countries with ATT as the mainstay of treatment. Moreover, we outline the recent progress of HDT development in the pulmonary TB field and discuss the possibility of its applicability to TB-uveitis. The concept of HDT might help direct future development of efficacious therapy for TB-uveitis, although more in-depth research on the immunoregulation of this disease is still necessary.

Anti-tubercular therapy in the treatment of tubercular uveitis: A systematic review and meta-analysis

We quantitatively evaluated the efficacy of antitubercular therapy (ATT) in tubercular uveitis (TBU) patients. Main outcome measures include inflammation recurrence, inflammation reduction, complete resolution of inflammation, improved visual acuity (VA), ability to taper corticosteroids to < 10 mg/day without inflammatory progression, and use of adjunctive immunosuppressants while on ATT. This review is prospectively registered in PROSPERO (CRD42020206845). Forty-nine studies reporting data for 4,017 TBU patients were included. In comparative studies, the odds ratio (OR) of inflammatory recurrence was 0.33 (95%CI:0.19-0.60) for TBU patients treated with ATT±corticosteroid versus no ATT. For TBU patients treated with ATT±corticosteroid, the pooled absolute incidences of inflammatory recurrence, inflammatory reduction, complete resolution of inflammation, and visual acuity improvement were 13% (n=310/2,216; 95%CI:9-18), 81% (n=217/276; 95%CI: 62-95), 83% (n=1,167/1,812; 95%CI: 77-89), and 65% (n=347/542; 95%CI:51-78), respectively. Corticosteroids were tapered to <10 mg/day without inflammatory progression in 91% (n=326/395; 95%CI:78-99) of patients, 9% (n=121/1,376; 95%CI:6-13) of whom were administered concomitant immunosuppressive agents alongside ATT. We conclude that treatment of TBU with ATT±corticosteroid is associated with a high level of control or improvement of inflammation. More prospective studies with detailed reporting of ATT regimens, patient subgroups, and outcomes are required to better evaluate ATT effectiveness.

Global prevalence and clinical outcomes of tubercular uveitis: a systematic review and meta-analysis

Tubercular uveitis (TBU) is an inflammation/infection of the eye secondary to Mycobacterium tuberculosis infection. The difficulty in making the diagnosis has resulted in variable prevalence and clinical response rates. We aimed to determine the global prevalence of TBU in uveitis patients stratified by TB high-burden countries (HBCs) and non-HBCs and by geographic regions and the clinical response of TBU to antitubercular treatment We performed a systematic review and meta-analysis of TBU studies published in PubMed, Scopus and EMBASE, up to June 30, 2020. A random effects model was used for all meta-analyses. Of 5,018 articles identified, 70 prevalence studies (65,607 uveitis and 3,166 TBU cases) and 18 clinical outcome studies (1,570 TBU cases; 1,304 responded to anti-tubercular therapy [ATT]) were analyzed. The overall weighted prevalence of TBU was 4.0% (95% CI, 3-5); in TB HBCs it was 7.0% (95% CI, 5-11), non-HBCs 3.0% (95% CI, 2-4), and sub-Saharan Africa 11.0% (95% CI, 8-15). The overall weighted clinical response was 82.0% (95% CI, 75-89). Despite the difficulty in diagnosing TBU, the prevalence is expectantly higher in HBCs, and sub-Saharan Africa and the clinical outcome is poor. Standardization of diagnostic criteria and ATT is warranted in future cohort studies.

Proteomic profile of vitreous in patients with tubercular uveitis

OBJECTIVE

To elucidate disease-specific host protein profile in vitreous fluid of patients with intraocular inflammation due to tubercular uveitis (TBU).

METHODS

Vitreous samples from 13 patients with TBU (group A), 7 with non-TBU (group B) and 9 with no uveitis (group C) were analysed by shotgun proteomics using Liquid Chromatography Tandem Mass Spectrometry (LC-MS/MS). Differentially expressed proteins (DEPs) were subjected to pathway analysis using WEB-based Gene SeT Analysis Toolkit software.

RESULTS

Compared to control groups (B + C combined), group A (TBU) displayed 32 (11 upregulated, 21 downregulated) DEPs, which revealed an upregulation of coagulation cascades, complement and classic pathways, and downregulation of metabolism of carbohydrates, gluconeogenesis, glucose metabolism and glycolysis/gluconeogenesis pathways. When compared to group B (non-TBU) alone, TBU displayed 58 DEPs (21 upregulated, 37 downregulated), with an upregulation of apoptosis, KRAS signaling, diabetes pathways, classic pathways, and downregulation of MTORC1 signaling, glycolysis/gluconeogenesis, and glucose metabolism.

CONCLUSION

This differential protein profile provides novel insights into the molecular mechanisms of TBU and a baseline to explore vitreous biomarkers to differentiate TBU from non-TBU, warranting future studies to identify and validate them as a diagnostic tool in TBU. The enriched pathways generate interesting hypotheses and drive further research.

IS1081-based Multi-targeted LAMP: An Opportunity to Detect Tubercular Uveitis

BACKGROUND

- Timely and accurate diagnosis of tubercular uveitis (TBU) is imperative, hence multitargeted loop-mediated isothermal amplification (MLAMP) using three gene targets (IS1081, IS6110 and MPB64) was evaluated for it.

METHODS

- About 120 vitreous fluid samples [70 clinically suspected TBU (3 culture-positive, 67 culture-negative) and 50 controls] were subjected to MLAMP to evaluate its performance in diagnosing TBU.

RESULTS

- Overall, the sensitivity, specificity, PPV and NPV of MLAMP in the diagnosis of TBU was 77.14%, 100%, 100% and 75.75%, respectively, with an additional detection of 9 (12.85%) cases (5 by IS1081LAMP and 2 each by MPB64LAMP and IS6110LAMP). Maximum TBU cases were detected by IS1081LAMP (50/70) followed by MPB64LAMP (47/70) and IS6110LAMP (45/70).

CONCLUSION

- MLAMP, with the incorporation of IS1081, served as a sensitive, rapid, simple and cost-effective technique for TBU diagnosis.

Immune Profiling of T Cells Infiltrating Vitreous Humor in Tubercular Uveitis

PURPOSE

To assess cellular composition and local cytokine response in vitreous humor of tubercular uveitis.

METHODS

Cells were collected from vitreous cassettes and peripheral blood of 8 tubercular uveitis and 5 control subjects, undergoing vitrectomy and analyzed by flow cytometry for cellular composition, activation status, proinflammatory cytokine expression, and uptake of TLR9 ligand, CpG ODN 2216.

RESULTS

CD3 + T cells with equal proportion of CD4+ and CD8 + T cells formed major fraction of infiltrating cells. The vitreous humor showed higher expression of recent activation marker, CD69, and proinflammatory cytokines, IFN-γ and IL-17A, in CD4 + T cells as compared to peripheral blood. Lastly, intraocular CD4 + T cells showed reduced uptake of ODN 2216 than peripheral blood.

CONCLUSIONS

Our results indicate that local antigenic stimuli trigger T cell infiltration and activation of CD4 + T cells that are hyporesponsive to TLR9 stimulation. These infiltrating T cells might be responsible in further aggravating ocular inflammation.

Diagnosis of tubercular uveitis by quantitative polymerase chain reaction

Purpose

To report the use of real-time or quantitative polymerase chain reaction (qPCR) in confirming the diagnosis of tubercular uveitis.

Methods

A qPCR assay using primers targeting the MPB64 gene of Mycobacterium tuberculosis (MTB) was developed. A standard curve for quantification of mycobacterial load was generated. Vitreous fluid samples from patients presumed to have tubercular uveitis were assayed to identify and quantify the mycobacterial load. The amount of the test sample product was interpolated from the standard curve of cycle threshold values generated from known starting copy number of standard MTB DNA.

Results

The copies of MTB genomes in the three test samples studied were found to be 7.61 × 10⁴, 4.53 × 10⁴, and 1.43 × 10⁵, respectively.

Conclusion

qPCR detected and quantified MTB genome from the vitreous fluid of eyes clinically suspected with tubercular uveitis.