Free light chains of immunoglobulins in patients with systemic sclerosis: correlations with lung involvement and inflammatory milieu

Aim Humoral immunity and b cells are thought to play an important role in the pathophysiology of the systemic sclerosis (SSc). The production of free light chains (FLC) of immunoglobulins is abnormally high in several pathological autoimmune conditions and reflects B cell activation. Furthermore, FLCs demonstrated different biological activities including their capability to modulate the immune system, proteolytic activity and complement cascade activation. The aims of this study are to determine the FLC levels in patients with SSc compared with healthy controls (HC) and to study their possible association with organ involvement and disease characteristics. Methods Sixty-five patients with SSc and 20 HC were studied. Clinical and immunological inflammatory characteristics were assessed for all the patients with SSc. kappa-FLC and lambda-FLC, interleukin 6 (IL-6) and B cell activating factor levels were measured. Results The mean serum kappa-FLC levels and FLC ratio were significantly higher in patients with SSc compared with HC, while the serum lambda-FLC levels were comparable. The levels of FLC were comparable in patients with diffuse skin disease and limited skin involvement, while kappa-FLC levels were increased in patients with restrictive lung (forced vital capacity (FVC) <80%) disease (26.4 +/- 7.4 mg/L) when compared with patients with FVC >= 80% (19.6 +/- 7.3 mg/L, P=0.009). In patients with SSc, the levels of serum kappa-FLC level directly correlated with the IL-6 levels (R=0.3, P=0.001) and disease activity (R=0.4, P=0.003). Conclusions FLC levels are elevated in SSc and high levels are associated with lung involvement and with a higher degree of inflammation, supporting a possible role of B cell activation in the pathophysiology of the disease.