FcγRIII-Mediated Production of TNF-α Induces Immune Complex Alveolitis Independently of CXC Chemokine Generation

We recently demonstrated a codominant role of C5aR and FcgammaRIII in the initiation of IgG immune complex-mediated inflammation in mice. In this study, we investigated the relative contribution of FcgammaRIII in the generation of several cytokines during experimental hypersensitivity pneumonitis/alveolitis in vivo. Induction of immune complex-alveolitis in C57BL/6 mice resulted in strong accumulation of neutrophils into the lung and enhanced chemotactic activity within bronchoalveolar lavage fluid accompanied by an increased production of the proinflammatory cytokines TNF-alpha and IL-1beta as well as the ELR-CXC chemokines macrophage inflammatory protein-2 (MIP-2) and cytokine-induced neutrophil chemoattractant (KC). FcgammaRIII-deficient C57BL/6 mice (FcgammaRIII(-/-)) showed a marked reduction of the inflammatory response due to decreased production of TNF-alpha, IL-1beta, and MIP-2. Results obtained in C57BL/6 mice either lacking the TNF-alpha class I receptor (TNF-alphaRI(-/-)) or treated with neutralizing anti-TNF-alpha mAb demonstrated an essential contribution of TNF-alpha for mediating IL-1beta release, neutrophil influx, and hemorrhage. Surprisingly, MIP-2 and KC chemokine levels remained largely unaffected in TNF-alphaRI(-/-) mice or after functional inhibition of TNF-alpha. These data suggest that in immune complex alveolitis, the activation of FcgammaRIII may induce divergent downstream effector pathways with TNF-alpha acting independently of CXC chemokines to trigger the inflammatory response in C57BL/6 mice.