Occurrence of Transmembrane Protein 119 in the Retina is Not Restricted to the Microglia: An Immunohistochemical Study.

Purpose: Recently, a new marker protein for microglial cells in the brain was postulated, transmembrane protein 119 (TMEM119), raising the hope for a new opportunity to reliably and unambiguously detect microglial cells in histologic sections. It was of interest whether TMEM119 also was a reliable microglial marker in the retina.

Methods: Anti-TMEM119 antibodies of two providers were used to label microglia in the murine retina, and labeling properties were compared to those of antibodies against Iba1 and CD11b. As an example of a pathologic situation, labeling for TMEM119 was also performed in eyes treated by an argon laser as an experimental model for choroidal neovascularization.

Results: TMEM119 immunoreactivity (IR) was found on microglial cells in the naïve retina. However, specificity and sensitivity of TMEM119 IR varied clearly depending on the source of the antibody, age of the mouse, and location of retinal microglia. After laser treatment, however, microglial cells lost their IR for TMEM119 at the site of the laser spot. Moreover, other cells became positive for TMEM119; for example, Müller cells.

Conclusions: TMEM119 is a useful marker for the microglia in the brain. However, retinal microglia shows variable IR for TMEM119, and the microglia is not the only cell showing TMEM IR. Therefore, TMEM119 appears not to be applicable as a general marker for the retinal microglia in pathologic situations.

Translational Relevance: Reliable detection and quantification of microglial cells is of high importance to study disease mechanisms and effects of therapeutic approaches in the retina.