Immunoglobulin free light chains in adult atopic dermatitis patients do not correlate with disease severity

BACKGROUND Although total IgE levels have been proposed as a biomarker for disease severity in atopic dermatitis (AD) and are increased in the majority of AD patients, they do not correlate with disease severity during short-term follow-up. During the synthesis of immunoglobulins, free light chains (Ig-FLCs) are produced in excess over heavy chains. In comparison with IgE molecules, Ig-FLCs have a very short serum half-life. Therefore, Ig-FLCs might be more suitable as a biomarker for disease severity during follow-up. Recent studies showed increased serum levels of kappa Ig-FLCs in infants with AD, correlating with disease severity. The aim of this study was to investigate serum kappa Ig-FLC levels in adults with AD, and their correlation to disease severity. METHODS Serum kappa If-FLC and total IgE levels were measured in 82 moderate to severe AD patients and 49 non-atopic controls. Blood was collected from patients before start of treatment with potent topical steroids (European classification: III-IV). 32 patients were treated during a clinical admission, and in this subpopulation a second blood sample was taken after 2 weeks of treatment. Clinical severity was determined by the Six Area Six Sign Atopic Dermatitis (SASSAD) severity score and a panel of serum biomarkers, including thymus and activation-regulated chemokine (TARC). RESULTS Serum kappa Ig-FLCs levels in adult AD patients were not increased compared to non-atopic controls. Moreover, we observed no correlation between kappa Ig-FLC serum levels and disease severity determined by SASSAD and a panel of serum biomarkers, including TARC. Serum kappa Ig-FLC levels did also not decrease during treatment. CONCLUSION There are no differences in serum kappa Ig-FLC levels between adult patients suffering from moderate to severe AD compared to non-atopic controls. Moreover, serum levels of kappa Ig-FLCs cannot be used as a biomarker for disease severity in adult AD.