CD3+CD4-CD8- Double-Negative Lymphocytes Are Increased in the Aqueous Humor of Patients with Retinitis Pigmentosa: Their Possible Role in Mediating Inflammation

Recently, evidence has supported a significant role for immune and oxidative-mediated damage underlying the pathogenesis of different types of retinal diseases, including retinitis pigmentosa (RP). Our study aimed to evaluate the presence of immune cells and mediators in patients with RP using flow cytometric analysis of peripheral blood (PB) and aqueous humor (AH) samples. We recruited 12 patients with RP and nine controls undergoing cataract surgery. Flow cytometric analysis of PB and AH samples provided a membrane staining that targeted surface molecules (CD14, CD16, CD19, CD3, CD4, CD8, and CD161) identifying monocytes, natural killer (NK) cells, B cells, T cells, and T subpopulations, respectively. Moreover, lymphocytes were polyclonally stimulated to evaluate cytokine (CK) production at single-cell level. The circulating immune cell distribution was comparable between patients with RP and controls. Conversely, in the AH of controls we could detect no cells, while in the RP AH samples we found infiltrating leukocytes, consisting of T (CD3+), B (CD19+), NK (CD16+CD3-) cells, and monocytes (CD14+). In patients with RP, the frequency of most infiltrating immune cell populations was similar between the AH and PB. However, among T cell subpopulations, the frequency of CD3+CD4+ T cells was significantly lower in the RP AH compared to RP PB, whereas CD3+CD4-CD8- double-negative (DN) T cells were significantly higher in the RP AH compared to RP PB. Cytokine production analysis revealed a trend toward an increased frequency of CD3+CD8-CD161+IFN-ɣ-producing cells and a decreased frequency of CD3+CD8+IL-4-producing cells in the RP AH compared to RP PB. The detection of immune cells, particularly DN T cells, and a Th1-skewed phenotype in RP AH suggests immune-mediated and inflammatory mechanisms in the disease.