Secretory leukocyte protease inhibitor (SLPI), a multifunctional protein in the host defense response

• SLPI plays a critical role in regulating host defense responses through multiple mechanisms.
• SLPI restrains excessive responses to microbiota at epithelial body barriers.
• SLPI controls microbial infection through its effects on microbes and the host.
• SLPI exhibits anti-inflammatory properties in allergy and autoimmunity.
• SLPI controls key steps of wound healing.
• SLPI regulates cell renewal, differentiation and apoptosis.

Secretory leukocyte protease inhibitor (SLPI), a ∼12 kDa nonglycosylated cationic protein, is emerging as an important regulator of innate and adaptive immunity and as a component of tissue regenerative programs. First described as an inhibitor of serine proteases such as neutrophil elastase, this protein is increasingly recognized as a molecule that benefits the host via its anti-proteolytic, anti-microbial and immunomodulatory activities. Here, we discuss the diverse functions of SLPI. Moreover, we review several novel layers of SLPI-mediated control that protect the host from excessive/dysregulated inflammation typical of infectious, allergic and autoinflammatory diseases and that support healing responses through affecting cell proliferation, differentiation and apoptosis.

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