Retinal pigment epithelial cells control early Mycobacterium tuberculosis infection via interferon signaling

PURPOSE. Mycobacterium tuberculosis (Mtb) bacilli have been found in retinal pigment epithelial (RPE) cells from uveitis patients without signs of systemic tuberculosis (TB) infection. RPE cells are important for ocular immune privilege and uveitis development.
METHODS. To address a potential role for Mtb-infected RPE cells in the development of uveitis, we delineated the response to Mtb infection in human RPE cells and primary human macrophages, the main target cell of Mtb. Primary human RPE cells, the human RPE cell line ARPE-19, and monocyte-derived proinflammatory M1 and anti-inflammatory M2 macrophages were infected with DsRed-expressing Mtb strain H37Rv. Infection rates and clearance were addressed along with RNA sequencing analysis, a confirmation analysis by dual-color reverse-transcriptase multiplex ligation-dependent probe amplification (dcRT-MLPA) and cytokine secretion.
RESULTS. RPE cells robustly controlled intracellular outgrowth of Mtb early after infection. The response in RPE cells to control Mtb survival was dominated by interferon (IFN) signaling and further characterized by prominent regulation of cell death/survival–associated genes and low-level production of Th1-associated cytokines. In contrast, macrophages engaged a plethora of responses including IFN signaling and communication between innate and adaptive immune cells to induce granuloma formation.
CONCLUSIONS. Together, our data demonstrate that RPE cells display a strong response to Mtb infection that appears, however, incomplete in comparison to the macrophage response to Mtb. The RPE response might reflect a balance between mechanisms aimed at Mtb eradication and mechanisms that limit retinal inflammation.