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SLPI, a potent epithelial and myeloid-derived serine protease inhibitor with antimicrobial and anti-inflammatory functions, is induced by the intracellular parasite Leishmania major, and increased SLPI expression is evident within lesions that follow L. major infection. In contrast to self-resolving infection in C57Bl/6 WT mice, Slpi−/− mice launch a strong Th1 response to L. major, yet fail to control infection and develop destructive, nonhealing lesions with systemic spread of parasites. Because SLPI is both produced by murine macrophages and antagonizes their function, we examined the contribution of macrophage polarization to the defective host response in the absence of SLPI. Slpi−/− and Slpi+/+ macrophages were first primed with either IFNγ or IL-4 to generate classically activated M1 or alternatively activated M2 macrophages. After infection with L. major, Slpi−/− M1 macrophages expressed elevated iNOS RNA, whereas arginase was more highly expressed in WT than Slpi−/− M2 macrophages. After in vivo infection, we found that both IFNγ and iNOS were persistently overexpressed in chronic lesions in Slpi−/− mice, but surprisingly, IL-4 and arginase concomitantly remained elevated. Moreover, overexpression of the negative regulators SOCS1 and IL-27 provided insight into the failure of IFNγ to clear L. major from the dermal lesions. Notably, adenoviral delivery of SLPI to L. major-infected Slpi−/− mice significantly limited the progression of infection. These studies suggest that convergence of M1 and M2 macrophage responses may influence the outcome of innate host defense against intracellular parasites and that SLPI is critical for coordinating resistance to chronic leishmaniasis.

Impaired wound healing states lead to substantial morbidity and cost with treatment resulting in an expenditure of billions of dollars per annum in the U.S. alone. Both chronic wounds and impaired acute wounds are characterized by excessive inflammation, enhanced proteolysis, and reduced matrix deposition. These confounding factors are exacerbated in the elderly, in part, as we report here, related to increased local and systemic tumor necrosis factor-alpha (TNF-α) levels. Moreover, we have used a secretory leukocyte protease inhibitor (SLPI) null mouse model of severely impaired wound healing and excessive inflammation, comparable to age-related delayed human healing, to demonstrate that topical application of anti-TNF-α neutralizing antibodies blunts leukocyte recruitment and NFκB activation, alters the balance between M1 and M2 macrophages, and accelerates wound healing. Following antagonism of TNF-α, matrix synthesis is enhanced, associated with suppression of both inflammatory parameters and NFκB binding activity. Our data suggest that inhibiting TNF-α is a critical event in reversing the severely impaired healing response associated with the absence of SLPI, and may be applicable to prophylaxis and/or treatment of impaired wound healing states in humans.

Secretory leukocyte protease inhibitor (SLPI) is a serine protease inhibitor with anti-microbial properties found in mucosal fluids. It is expressed during cutaneous wound healing. Impaired healing states are characterized by excessive proteolysis and often bacterial infection, leading to the hypothesis that SLPI may have a role in this process. We have generated mice null for the gene encoding SLPI (Slpi), which show impaired cutaneous wound healing with increased inflammation and elastase activity. The altered inflammatory profile involves enhanced activation of local TGF-beta in Slpi-null mice. We propose that SLPI is a pivotal endogenous factor necessary for optimal wound healing.