Background/Purpose:

A potential  mechanism for the vasculopathy of Juvenile Dermatomyositis (JDM), the most common pediatric inflammatory myopathy, has been attributed to complement mediated immune complex damage to endothelial cells with subsequent release of von Willebrand Factor Antigen (vWF:Ag).  Although we previously reported that JDM C4 levels were  decreased in  30% patients, associated with decreased gene copy number  [Arthritis Rheum, 2012;  64(S10):S826], the role of C4 in this process has not been documented.   The purpose of this cross-sectional study was to determine the concentration of immune complexes in JDM sera compared with healthy controls and their association with levels of C4, duration of illness, disease activity scores, vWF:Ag , and absolute number of natural killer cells (NKs)– previously found to be decreased in active disease in 55.7% of JDM.

Methods:

62 children with definite JDM and 20 healthy controls were enrolled and their sera were obtained for immune complex measurement. Among the JDM patients, 29 had normal levels of C4 (21 girls and 8 boys; mean age 14.7±6.8 years) and 32 had low C4 (22 girls and 10 boys, mean age 15.0±3.8 years).  The healthy control group was composed of 11 girls and 9 boys, mean age 12.5±3.5 years. Immune complex level, measured as an aggregated human γ-globulin equivalent, was determined by ELISA. The association of immune complex levels with clinical variables was determined:  disease activity scores (DAS, skin, muscle, total score), duration of untreated disease (DUD), and  vWF:Ag.  ANOVA was used to test the difference of immune complex levels among low, normal C4, and control groups. The Tukey post-hoc was used to test the pair-wise mean difference.

Results:  

The immune complex level in pediatric healthy controls was 317±332.4 μg/mL (n=20) (AHG equivalent), 506±347 μg/mL in JDM with low C4 (n=32) and 534±350 μg/mL in JDM with normal C4 (n=29).  The immune complex levels in JDM with low or normal C4 was significantly higher than that in healthy controls (p=0.01). However, there was no difference in the immune complex levels between children with JDM with low C4 and JDM with normal C4 levels (p=0.99). Furthermore, no significant correlation was observed between immune complex levels and a range of clinical features, including duration between disease onset and first treatment (p=0.99), DAS skin (p=0.14), DAS muscle (p=0.15), DAS total (p=0.25), level of vWF:Ag  (p=0.86), or  between  immune complex level and the absolute NK count (p=0.29) among the patients with JDM.

Conclusion:  

We conclude that that immune complex levels are increased in children with JDM irrespective of C4 levels and are not associated with disease duration, activity or evidence of vascular damage. It is not known if these immune complexes are antigenic, or if they play a role in the initiation or perpetuation of disease.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/increased-immune-complex-levels-in-children-with-juvenile-dermatomyositis-are-not-associated-with-levels-of-von-willebrand-factor-antigen-c4-duration-of-illness-disease-activity-score-or-the-absol/