Immunohistological characterization of equine synovial tissue in metacarpophalangeal joints of different ages and osteoarthritis status.

OBJECTIVE

Synovial macrophages' role in equine osteoarthritis (OA) is not well understood, despite horses being a model for human degenerative joint disorders. Equine synovial macrophages' characterization is limited and age-related changes are not described. This study aimed to evaluate surface marker distribution and expression from potential synovial tissue macrophages in foals, adult non-affected, and OA-affected horses.

METHODS

Surface markers (CD14, CD16, CD206) were quantitatively evaluated on dorsal villous synovial biopsies from the metacarpophalangeal joint of foals (F), non-affected (control; CTRL), and OA-affected adults (OA) using immunofluorescence histology and computed image analysis. Samples were analyzed in three regions: intimal cell layer (ICL), subintimal tissue layer of the villous region (SI-V), and subintimal tissue layer not associated with the villous region (SI-N). Synovial fluid protein, cytokine, and chemokine concentrations, and hematoxylin-eosin (HE) staining were performed to assess joint disease state.

RESULTS

Marker-associated areas were increased in ICL and SI-V compared to SI-N for all three groups. The CD14+ area was increased in the CTRL when compared to the OA and F groups (ICL, SI-V). CD16+ areas were similar in all groups, while CD206+ area was larger in foals compared to CTRL and OA groups (ICL, SI-V). Synovial fluid cytokine and chemokine concentrations did not differ between groups.

CONCLUSIONS

Computed analysis of immunofluorescence staining of CD14, CD16, and CD206 on equine synovial tissue revealed region specific marker expressions. While an altered marker expression in relation to age and degenerative joint disease was shown, further investigation is required to determine marker significance for identifying equine synovial tissue macrophages.