Bruce A. Jacobson

Regulation and Function of the Interleukin 13 Receptor α 2 During a T Helper Cell Type 2–dominant Immune Response

Highly polarized type 2 cytokine responses can be harmful and even lethal to the host if they are too vigorous or persist too long. Therefore, it is important to elucidate the mechanisms that down-regulate these reactions. Interleukin (IL)-13 has emerged as a central mediator of T helper cell (Th)2-dominant immune responses, exhibiting a diverse array of functional activities including regulation of airway hyperreactivity, resistance to nematode parasites, and tissue remodeling and fibrosis. Here, we show that IL-13 receptor (R)α2 is a critical down-regulatory factor of IL-13–mediated tissue fibrosis induced by the parasitic helminth Schistosoma mansoni. IL-13Rα2 expression was induced after the onset of the fibrotic response, IL-10, IL-13, and Stat6 dependent, and inhibited by the Th1-inducing adjuvant IL-12. Strikingly, schistosome-infected C57BL/6 and BALB/c IL-13Rα2–deficient mice showed a marked exacerbation in hepatic fibrosis, despite displaying no change in granuloma size, tissue eosinophilia, or mastocytosis. Fibrosis increased despite the fact that IL-13 levels decreased significantly in the liver and serum. Importantly, pathology was prevented when IL-13Rα2–deficient mice were treated with a soluble IL-13Rα2-Fc construct, formally demonstrating that their exacerbated fibrotic response was due to heightened IL-13 activity. Together, these studies illustrate the central role played by the IL-13Rα2 in the down-regulation of a chronic and pathogenic Th2-mediated immune response.

Enhanced Interleukin (IL)-13 Responses in Mice Lacking IL-13 Receptor α 2

Interleukin (IL)-13 has recently been shown to play important and unique roles in asthma, parasite immunity, and tumor recurrence. At least two distinct receptor components, IL-4 receptor (R)α and IL-13Rα1, mediate the diverse actions of IL-13. We have recently described an additional high affinity receptor for IL-13, IL-13Rα2, whose function in IL-13 signaling is unknown. To better appreciate the functional importance of IL-13Rα2, mice deficient in IL-13Rα2 were generated by gene targeting. Serum immunoglobulin E levels were increased in IL-13Rα2−/− mice despite the fact that serum IL-13 was absent and immune interferon γ production increased compared with wild-type mice. IL-13Rα2–deficient mice display increased bone marrow macrophage progenitor frequency and decreased tissue macrophage nitric oxide and IL-12 production in response to lipopolysaccharide. These results are consistent with a phenotype of enhanced IL-13 responsiveness and demonstrate a role for endogenous IL-13 and IL-13Rα2 in regulating immune responses in wild-type mice.

Human Alveolar Macrophage Gene Responses to Mycobacterium tuberculosis Strains H37Ra and H37Rv

H37Rv and H37Ra have been widely used as models of virulent and avirulent strains, respectively, of Mycobacterium tuberculosis. Since the sequencing of H37Rv, microarrays have been used to investigate gene expression of M. tuberculosis strains under various conditions, and to compare gene expression of specific isolates of the organism. Because differences in the virulence of these organisms could also be manifest via their differential induction of host genes, we used Affymetrix Human Genome Arrays U133A and U133B to evaluate human alveolar macrophage (AM) responses to infection with H37Rv and H37Ra. H37Rv altered expression of far more genes than did H37Ra. Moreover, the genes induced by H37Rv to a greater extent than by H37Ra were predominantly associated with the development of effective immunity. H37Rv markedly increased expression of IL-23 p19, whereas neither organism significantly induced IL-12 p35 expression. Quantitative PCR confirmed that H37Rv induced significantly more AM p19 expression than did H37Ra. After low-level infection of both AM and peripheral blood monocytes (MN) with H37Rv, neither cell type produced IL-12 (by ELISA). In contrast, AM displayed significant IL-23 production in response to H37Rv, whereas MN did not. Our findings thus suggest an important role for IL-23 in human host responses to pulmonary infection with M. tuberculosis, and are consistent with epidemiologic and genetic studies that imply that H37Rv may not have unusual capacity to cause human disease.

Characterization of MMP-9 and -12 KO mice in a model of acute smoke exposure

Short-term cigarette smoke exposure in mice has been shown to exhibit some similarities to cell and cell-mediated inflammation seen in COPD patients. We sought to identify biomarkers in the lungs and bronchoalveolar lavage fluid (BALF) that would characterize this inflammation. Mice were exposed; nose only, to 600 mg/m3 of cigarette smoke from 2R4F Kentucky Reference cigarettes twice daily for three consecutive days. Sham smoked animals were exposed to room air. Short-term cigarette smoke exposure induced a mild but statistically significant increase in total BAL cells in addition to a significant increase in neutrophils as compared with sham-exposed animals. Oral administration of dexamethasone did not attenuate total BAL cell or neutrophil counts. However, administration of an oral PDE4 inhibitor, significantly reduced percent neutrophil and macrophage counts. To assess expression of genes involved in this model, transcriptional profiling was performed on whole lungs harvested on day 4. Genes with the greatest fold increase included SAA3, CXCL1, 2 and 5 and NOXO1. In addition, multiplex analysis of BALF collected on day 4, revealed significant elevation in inflammatory mediators including cytokines, chemokines and metalloproteinases. Matrix metalloproteinase (MMP)–9 and –12 knockout (KO) mice were also tested in this model to evaluate whether or not these deficiencies influence acute smoke-induced inflammation. Total BAL inflammation and neutrophil counts were decreased in smoke exposed MMP-9 and -12 KO mice compared to wild type controls. These effects, however seem to be strain dependent as they were noted only in BALB/c KO animals. Deficiencies in MMP-9 and –12 appear to be beneficial in having an anti-inflammatory effect following acute exposure to smoke.