Role of Interleukin-6 in Immune Complex Induced Models of Vascular Injury

Previous studies have suggested that Interleukin-6 (IL-6) acts as a marker of vasculitis. To determine the role of IL-6 in vasculitis we utilized two models of immune complex induced vascular injury (dermal Arthus and acute pulmonary alveolitis) in IL-6 deficient (IL-6^−/−) and IL-6 sufficient (IL-6^+/+) mice. Plasma and bronchoalveolar lavage (BAL) levels of IL-6 were elevated in the injured IL-6^+/+ mice with acute alveolitis and in the plasma of IL-6^+/+ mice with dermal Arthus vasculitis. While, IL-6 levels in IL-6^−/− mice were near or below the levels of detection. Histological examination of the intensity of vascular injury response demonstrated no significant differences between IL-6^−/− and IL6^+/+ mice. More specifically, lung permeability (total protein in the BAL) in the lung injury model in IL-6^−/− mice was the same as injured IL-6^+/+ mice. As a corollary, assessment of vascular permeability in both models was the same in the IL-6^−/− as the IL-6^+/+ mice. Quantification of leukocyte influx into the injured tissues in both models also revealed no differences between the IL-6^−/− and IL-6^+/+ mice. These data demonstrate that while IL-6 is upregulated in acute vascular injury it does not appear to be critical in the development of the vascular inflammatory response.