Abstract
IntroductionComplexes between cartilage oligomeric matrix protein (COMP) and the complement activation product C3b have been found in the circulation of patients with rheumatoid arthritis and systemic lupus erythematosus. In systemic sclerosis (SSc) COMP expression in the skin is upregulated both in lesional and non-lesional skin, which is also reflected in an increased amount of circulating COMP. We investigated the presence of COMP-C3b complexes in serum and skin biopsies of patients with SSc.MethodsThe presence of COMP and COMP-C3b complexes in the serum of 80 patients with limited cutaneous SSc (lcSSc, n = 40) and diffuse cutaneous SSc (dcSSc, n = 40) and 97 healthy controls was measured by ELISA and correlated to different clinical parameters. Samples were collected both at baseline and after three to five years to assess longitudinal changes in COMP-C3b complex levels. Furthermore, skin biopsies from seven patients with dcSSc and three healthy controls were analyzed for expression of COMP and deposition of C3b and IgG.ResultsSerum levels of COMP-C3b were found to be elevated in both dcSSc and lcSSc compared to healthy controls and decreased at the second measurement in patients on immunosuppressive therapy. No co-localization of COMP and C3b was found in the skin biopsies, indicating that the COMP-C3b complexes are formed upon release of COMP into the circulation.ConclusionCOMP-C3b complexes are found in the serum of patients with SSc. The lack of co-localization between COMP and C3b in the skin suggests that COMP does not drive complement activation in the skin in SSc.
Highlights
Complexes between cartilage oligomeric matrix protein (COMP) and the complement activation product C3b have been found in the circulation of patients with rheumatoid arthritis and systemic lupus erythematosus
Levels of COMP-C3b complexes are elevated in systemic sclerosis (SSc) Both COMP and COMP-C3b levels were found to be elevated in the serum of SSc patients compared to healthy controls (P
There was a decrease in COMP-C3b in both Diffuse cutaneous systemic sclerosis (dcSSc) and limited cutaneous SSc (lcSSc) between the first and the second sample obtained (Figure 1C), this decrease was significant only for patients who were introduced to immunosuppressive treatment between the first and second sampling
Summary
Complexes between cartilage oligomeric matrix protein (COMP) and the complement activation product C3b have been found in the circulation of patients with rheumatoid arthritis and systemic lupus erythematosus. In systemic sclerosis (SSc) COMP expression in the skin is upregulated both in lesional and non-lesional skin, which is reflected in an increased amount of circulating COMP. We investigated the presence of COMP-C3b complexes in serum and skin biopsies of patients with SSc. Systemic sclerosis (SSc) is a multi-organ disease characterized by fibrosis of the skin and internal organs as well as vasculopathy [1]. Several studies have reported the presence of cartilage oligomeric matrix protein (COMP) in both lesional and non-lesional skin biopsies [4,5,6] as well as expression in cultured dermal fibroblasts from SSc patients [4,7]. A decreased expression of the complement inhibitors decay accelerating factor and membrane cofactor protein in the vascular endothelium has been observed in SSc, which might contribute to vascular damage and further to fibrosis [25]
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