Background: CD5 antigen-like (CD5L) is a circulating glycoprotein abundant in the blood. CD5L serum levels are elevated in several infectious and sterile inflammatory diseases. It is crucial for fighting infections [1].

Objectives: The study investigates biological processes related to CD5L in rheumatoid arthritis (RA).

Methods: CD5L levels were measured by ELISA (EH94RB, Invitrogen, Waltham, MA) in the serum of 87 randomly selected RA patients (age 62, disease duration 11 (6-22) years) and 11 healthy controls (age 58). A subset of RA patients had paired samples of serum and synovial fluid available for measuring CD5L. Aiming to investigate the relationship between serum CD5L levels and the transcriptomes of CD4 and CD14 cells, we used RNAseq of 35 RA patients. The transcriptomic analysis was done in lineal regression to the serum levels of CD5L, which identified differentially expressed genes in both CD4 and CD14 cell transcriptomes. Statistical analysis was done in Prism GraphPad version 10. Bioinformatic analysis was done using the R toolkits and iCellNET platform.

Results: We found that serum CD5L levels tended to be higher in RA patients than in controls ( p = 0.057). Comparing paired samples of serum and synovial fluid of 6 RA patients, we found a significant accumulation of CD5L levels inside the joints of RA patients. Serum CD5L levels were directly correlated to the disease activity measured by DAS28 (rho 0.31, p=0.006) and degree of radiographical damage quantified by vdH-Sharp score (rho 0.38, p=0.012). Additionally, serum CD5L correlated positively with IL6 (rho 0.326, p=0.054) and TNF (rho 0.422, p=0.012) production by cultured CD14 cells. We found no correlation between serum CD5L and production of TNF, IFNg and IL10 in CD4 cell cultures. These observations suggested that CD14, rather than CD4 cells, were sensitive to CD5L effects. Freshly isolated CD4 and CD14 cells of RA patients have low/unmeasurable expression of CD5L as measured on mRNA levels by RNAseq and on protein levels in cell culture supernatants. Thus, these cells are unlikely the source of CD5L measured in serum. To investigate the relationship between serum CD5L levels and the transcriptome of CD14 cells, we used RNAseq of 35 randomly selected RA patients. The transcriptomic analysis was done in lineal regression to the serum levels of CD5L, which identified 386 differentially expressed genes (DEG, basemean above 10, log2FC≥0.15) upregulated in CD14 cell transcriptome. The analysis revealed that CD5L levels were associated with a CD16+ CD14 cell phenotype characterized by the upregulation of cell cycle suppressing and cell interaction promoting adhesion molecules including CXC chemokine receptors and check-point receptors. Indeed, investigation of biological processes associated with DEG function revealed regulation of cell proliferation including CDKN1B, CDKN1B, CDC25B, JUN, JUNB, cellular adhesion controlling cells including CXCR3, CXCR6, and their ligands CXCL10 and CXCL16, respectively, and multiple immunological check-point receptors PDCD1/PD1L, TNFSF9/4-1BB ligand and its receptor TNFRSF9/CD137, TNFRSF18/GITR and TNFRSF21/DR6 genes, HLA-DRB1 and HLA-DQ genes. The molecules controlling intracellular localization and transport were presented by IGF2R, IFT122, LLGL2, VPS13D, SNX15, ZDHHC2, DYNC1H1. Common to all those BP were IFNG and FCGR3A. CD36 has been identified as a CD5L receptor. Ligation of CD36 receptor initiates PPARg signaling essential for BMP2-dependent bone remodeling. In conjunction to skeletal morphology, we observed a direct relationship between serum CD5L levels and the upregulated expression of pioneer transcription factors BMP2, KLF4, and RUNX2 in CD14+ cells, all critical regulators of the osteoclast and osteoblast differentiation. The upregulation of these transcription factors was combined by the executive network including CD36 ligand thrombospondin 1, uPA receptor (PLAUR) responsible for cell migration and invasion, BMP antagonist GREM2, serpin peptidase inhibitor SERPINE2, caveolin 1, laminin A (LMNA), all downstream of BMP2.

Conclusion: This study reveals an association between serum levels of CD5L and the anti-inflammatory and bone remodeling phenotype of CD14 cells, which could contribute to arthritis resolution.

REFERENCES: [1] Oliveira, L., et al., CD5L as a promising biological therapeutic for treating sepsis. Nat Commun, 2024. doi: 10.1038/s41467-024-48360-8.

Acknowledgements: NIL.

Disclosure of Interests: None declared.

© The Authors 2025. This abstract is an open access article published in Annals of Rheumatic Diseases under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ). Neither EULAR nor the publisher make any representation as to the accuracy of the content. The authors are solely responsible for the content in their abstract including accuracy of the facts, statements, results, conclusion, citing resources etc.