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Lung-Restricted Macrophage Activation in the Pearl Mouse Model of Hermansky-Pudlak Syndrome¹

Lisa R. Young^*,, Michael T. Borchers^*,, Holly L. Allen, Reta S. Gibbons and Francis X. McCormack^2,*

^* Department of Medicine, Division of Pulmonary and Critical Care, University of Cincinnati, Cincinnati, OH 45267; Department of Pediatrics, Division of Pulmonary Medicine, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH 45229; Department of Environmental Health, Division of Environmental Genetics and Molecular Toxicology, University of Cincinnati, Cincinnati, OH 45267; and Department of Medicine, Division of Infectious Diseases, University of Cincinnati, Cincinnati, OH 45267

Pulmonary inflammation, abnormalities in alveolar type II cell and macrophage morphology, and pulmonary fibrosis are features of Hermansky-Pudlak Syndrome (HPS). We used the naturally occurring "pearl" HPS2 mouse model to investigate the mechanisms of lung inflammation observed in HPS. Although baseline bronchoalveolar lavage (BAL) cell counts and differentials were similar in pearl and strain-matched wild-type (WT) mice, elevated levels of proinflammatory (MIP1) and counterregulatory (IL-12p40, soluble TNFr1/2) factors, but not TNF-, were detected in BAL from pearl mice. After intranasal LPS challenge, BAL levels of TNF-, MIP1, KC, and MCP-1 were 2- to 3-fold greater in pearl than WT mice. At baseline, cultured pearl alveolar macrophages (AMs) had markedly increased production of inflammatory cytokines. Furthermore, pearl AMs had exaggerated TNF- responses to TLR4, TLR2, and TLR3 ligands, as well as increased IFN-/LPS-induced NO production. After 24 h in culture, pearl AM LPS responses reverted to WT levels, and pearl AMs were appropriately refractory to continuous LPS exposure. In contrast, cultured pearl peritoneal macrophages and peripheral blood monocytes did not produce TNF- at baseline and had LPS responses which were no different from WT controls. Exposure of WT AMs to heat- and protease-labile components of pearl BAL, but not WT BAL, resulted in robust TNF- secretion. Similar abnormalities were identified in AMs and BAL from another HPS model, pale ear HPS1 mice. We conclude that the lungs of HPS mice exhibit hyperresponsiveness to LPS and constitutive and organ-specific macrophage activation.

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