Synovial fluid IL-16 and RANTES/CCL5 signals in early knee osteoarthritis: a pilot antibody-array study

Reliable molecular indicators for early osteoarthritis (OA) remain limited. Because synovial fluid (SF) reflects the intra-articular immune microenvironment, inflammatory signals may help describe preliminary features associated with early OA for future validation. This pilot, hypothesis-generating study used a high-throughput antibody array to profile SF cytokines across radiographic groups of knee OA.

Sixteen participants were included: a K-L grade 0 non-radiographic comparator group (K0, n = 4), early OA (K1; Kellgren-Lawrence grade 1-2, n = 6), and late OA (K3; grade 3-4, n = 6). Forty inflammatory proteins were measured using the RayBiotech Human Inflammation Antibody Array.

In K1 versus K0, IL-16 [fold change (FC) = 15.79; logFC = 3.98; approximate post hoc uncertainty interval for logFC, 2.21 to 5.75; adj.P.Val = 0.027] and RANTES/CCL5 (FC = 11.83; logFC = 3.56; approximate post hoc uncertainty interval for logFC, -1.23 to 8.36; adj. P.Val = 0.027) were the only proteins that remained significant after Benjamini-Hochberg correction. PCA and heatmap analyses based on selected proteins were used only as visualization of selected signals and not as evidence of diagnostic discrimination. In K3 versus K1, seven proteins showed exploratory downregulation based on raw P values but did not survive multiple-testing correction. GO/KEGG analyses were therefore interpreted as supplementary hypothesis generation only.

In this very small pilot cohort, IL-16 and RANTES/CCL5 showed array-based inflammatory signals associated with early OA after multiple-testing correction. The findings do not constitute validation of a clinical marker, and no diagnostic claim is made because ELISA confirmation, ROC analysis, and an independent validation cohort were not available. These data should therefore be regarded as preliminary discovery results, and larger, adequately powered studies with orthogonal quantitative validation are required before clinical translation can be considered.