Uveitis, a complex group of inflammatory eye diseases, presents significant therapeutic challenges due to its heterogeneous nature. In a recent study,1 we sought to identify fundamental mechanisms that drive ocular inflammation.
Cytokines are small molecules that influence the behavior of immune cells in specific ways. Current cytokine-targeted treatments for uveitis, such as adalimumab, only benefit a subset of patients, suggesting that immunologic mechanisms may not be identical between all forms of uveitis. In contrast, chemokines are broadly acting small molecules produced by immune cells, which recruit other immune cells to an inflamed tissue.
Given their potential for broad efficacy, we sought to identify the chemokines most relevant to diverse forms of ocular inflammation. To do this, we measured the levels and cell type–
specific gene expression of each chemokine in the aqueous fluid from patients with active uveitis. First, we compared the concentration of chemokines between the eye and blood to identify the molecules that could drive immune cells into the eye. Then, we mapped a network of chemokine production and response within the ocular immune cells.
Study Details
Our study1 involved analyzing aqueous and plasma protein concentrations, as well as single-cell gene expression from aqueous fluid biopsies. We compared a heterogeneous cohort of patients with active or inactive uveitis and healthy controls. The primary goal was to identify chemokines enriched in the eye during active uveitis as well as their cellular source.
The study identified 6 chemokines elevated in active uveitis compared to controls, and more enriched in aqueous fluid than in plasma: C-C motif chemokine ligand (CCL) 2, C-X-C motif chemokine ligand (CXCL) 10, CXCL9, CXCL8, CCL3, and CCL14. Notably, CCL2 and CXCL10 were consistently enriched in all patients, regardless of the disease subtype, severity, or treatment status. These conserved chemokine gradients were also found in mice, suggesting that murine inflammatory models may be useful for studying this process.
Single-cell RNA sequencing is an advanced technique that assesses the expression of 20,000 to 30,000 mRNA transcripts in individual cells. This approach significantly advances our ability to obtain meaningful information from very small ocular fluid biopsies. Using this technique, we found that macrophages were the primary source of CCL2 and CXCL10 in the aqueous fluid during uveitis and that these chemokines can interact with receptors on most of the immune cells present in the eye during uveitis.
Major Findings
Taken together, our results showed that ocular macrophages produce CCL2 and CXCL10, which in turn recruit additional immune cell types, including other macrophages, T cells, and B cells. This macrophage-driven CCL2/CXCL10 chemokine gradient is conserved across human uveitis disease types, and is also present in mice, suggesting it is a central mechanism driving ocular inflammation.
These findings suggest that targeting either macrophages or the chemokines they produce could offer a new broadly effective therapeutic strategy for uveitis. The conserved nature of CCL2 and CXCL10 gradients could inform the development of treatments that are effective across various uveitis subtypes and possibly other inflammatory conditions affecting the eye.
Conclusion
Understanding conserved inflammatory pathways in the eye is crucial for improving patient outcomes. This study highlights the central role of macrophages and the chemokines CCL2 and CXCL10 in the inflammatory process of uveitis. Targeting these chemokines and their sources could lead to new therapeutic strategies, which offer hope for efficacious uveitis treatments. RP
References
1. Lin JB, Pepple KL, Concepcion C, et al. Aqueous macrophages contribute to conserved CCL2 and CXCL10 gradients in uveitis. Ophthalmol Sci. 2023;4(4):100453. doi:10.1016/j.xops.2023.100453
