To determine the concentrations of surfactant protein (SP)-A and SP-D in synovial fluid samples from patients with rheumatoid arthritis and healthy controls and correlate them with rheumatoid factor, C-reactive protein (CRP), immunoglobulin (Ig) A, IgM, and IgG, total protein, and total lipid content.
The concentrations of SP-A, SP-D, CRP, IgA, IgM, IgG, and rheumatoid factor were measured in the synovial fluid of 7 patients with rheumatoid arthritis and 3 samples of healthy synovial fluid obtained at autopsy. The bands obtained by specific antibodies in Western blotting to determine the surfactant protein concentration were analyzed densitometrically and synovial fluid total phospholipids and protein content were analyzed spectrophotometrically.
Patients with rheumatoid arthritis had increased concentrations of proteins and lipids in the synovial fluid, which correlated with 3.5-fold increase in SP-A and 6.1-fold increase in SP-D concentrations. Total protein content in synovial fluid samples from patients with rheumatoid arthritis showed a 2.1-fold increase and phospholipid content showed 7.0-fold increase in comparison with samples of healthy synovial fluid. Rheumatoid factor, CRP, IgA, IgM, and IgG concentrations in synovial fluid samples from patients with rheumatoid arthritis were 40-2660 KIU/L, 4-35 mg/L, 0.10-2.70 g/L, 0.50-1.90 g/L, and 5.3-15.4 g/L respectively.
SP-A and SP-D were present and expressed in various degrees in the synovial fluid of patients with rheumatoid arthritis. SP-A and SP-D may play role in the initiation of immune system and joint inflammation, and may be an integral component of synovial fluid and provide insights for in innate and adaptive immunity within the joint.