Autoreactive T Cells in Immunopathogenesis of TB-Associated Uveitis

Intraocular inflammation in tuberculosis-associated uveitis (TBU) is usually widespread, and responds unpredictably to treatment. Herein, we analyze the intraocular T-cell response in TBU for its surface phenotype, antigenic specificity, and functional characteristics to explain the above observations.

We isolated T cells from vitreous humor samples of patients with TBU and non-TB uveitis (controls). These were directly stained for surface markers CD4, CD8, CD45RO, CD45RA, CCR7, as well as intracellular cytokines IFN-γ, TNF-α, and IL-17 and analyzed on flow cytometry. Antigenic specificity was determined by activating with Mycobacterium tuberculosis-specific antigen Early Secreted Antigenic Target-6 (ESAT-6) or retinal crude extract (RCE). Activation-induced cell death (AICD) characteristics of each T-cell population were analyzed by staining for PI-Annexin V, Fas-FasL, phospho-Akt, and phospho-Erk1/2.

Immunophenotyping of vitreous humor samples demonstrated polyfunctional effector and central memory CD4+ T helper cells coexpressing IFN-γ, TNF-α, and IL-17. Both ESAT-6 and RCE (autoreactive) specificity was found in T cells extracted from TBU samples; however, the mycobacterial and autoreactive T-cell populations differed in their sensitivity to AICD. Autoreactive T cells appeared to resist AICD through decreased expression of apoptotic markers, FasL and caspase-3, sustained phosphorylation of Akt, and lowered Erk1/2 activity.

Autoreactive T cells are present in TBU eyes and are relatively resistant to AICD. An understanding of this epiphenomenon could be crucial in planning treatment of TBU patients, and interpreting response to anti-TB therapy.