Anti-collagen antibodies and immune complexes in equine joint diseases.

An investigation was made into the possible contribution of autoimmune mechanisms to equine arthropathies. Serum and synovial fluid (SF) immune complexes and anti-collagen Type II antibodies were measured, by ELISA, in groups of horses with naturally occurring osteoarthritis (OA), osteochondritis dissecans (OCD), bone fracture, traumatised joints, synovitis, infected joints and non-diseased (control) joints. Significantly raised anti-collagen Type II antibodies were found in osteoarthritic (P < 0.02) and traumatised joint synovial fluids (P < 0.01) compared with the control, where ten of 38 (26%) OA and five of eight (63%) traumatised joint synovial fluid samples had raised anti-collagen Type II antibodies (above mean and 2 SD of control group; P < 0.05). Significantly raised levels of C1q-binding immune complexes were found in the synovial fluids of horses with OA (P < 0.001), OCD (P < 0.02), fractured articular bone (P < 0.001), infected (P < 0.01) and traumatised joints (P < 0.001) as compared with the control horses. Raised C1q-binding activity (above mean and 2 SD of control group; P < 0.05) was shown in synovial fluids in 18 of 38 (47%) OA, four of 16 (25%) OCD, four of nine (44%) fractured bone, one of eight (14%) synovitis, two of four (50%) infected joints and seven of eight (88%) traumatised joints. No raised anti-collagen Type II antibodies or C1q-binding activity were detected in sera from any clinical group. Correlations were found, in synovial fluids, between anti-collagen Type II antibodies and C1q-binding activity in OA (P < 0.02), synovitis (P < 0.01) and infected joint (P < 0.05) groups. Within individual horses, there were no correlations between the SF and sera measurements of either anti-collagen II or C1q-binding activity. The relationship between cause and effect of these immunological findings cannot be determined; as they are common to many types of equine joint disorder it is probable that they are not an initiating factor in pathology.