Smad3 regulates dermal cytokine and chemokine expression and specific antibody production in murine responses to a respiratory chemical sensitizer.

Background: The cytokine transforming growth factor-beta(TGF-beta) has important regulatory roles in the immune system. To investigate the role of intact TGF-beta signaling during the contact hypersensitivity (CHS) response to a respiratory allergen, we exposed Smad3-/- mice to topical trimellitic anhydride (TMA).

Methods: CHS was induced by topical application of TMA. The swelling of the TMA-exposed ears was analyzed, and lymph node, ear tissue and skin biopsies were collected for RNA isolation, histology and histochemical analyses. Lymph node cell proliferation was measured and blood samples were collected for analysis of TMA-specific immunoglobulin.

Results: Topical TMA exposure resulted in increased mRNA expression of proinflammatory and suppressive cytokines (IL-1beta, TNF-alpha, IL-6, IFN-gamma, IL-4, IL-10, IL-17, IL-23, TGF-beta), chemokines (CXCL9, CXCL10, CCL24) and chemokine receptors (CCR7, CCR8, CXCR2), increased numbers of CD3+ T cells in ear tissue, and lymphadenopathy in the Smad3-/- mice. The IL-10 result was confirmed at the protein level by immunohistochemistry. However, the ear-swelling response and infiltration of eosinophils, F4/80+ cells, CD11c+ cells and mast cells were similar in the Smad3-/- mice compared to their wild-type (WT) siblings. While TMA-specific IgE was induced equally in the WT and Smad3-/- mice, the concentration of TMA-specific IgG2a was significantly lower in the Smad3-/- mice.

Conclusions: The Smad3 molecule contributes significantly to the regulation of the cytokine and chemokine network during the CHS response to TMA. The lack of Smad3 resulted in a potent Th2 shift, confirmed by strongly impaired IgG2a levels.