Mite allergen induces nitric oxide production in alveolar macrophage cell lines via CD14/toll-like receptor 4, and is inhibited by surfactant protein D

Summary Background Previously, we have found that dust mite allergens can directly activate alveolar macrophages (AMs), induce inflammatory cytokines, and enhance T‐helper type 2 cytokine production. A molecule of innate immunity in the lung, surfactant protein D (SP‐D), is able to bind mite allergens and alleviates allergen‐induced airway inflammation. Objectives This study was aimed at investigating the activation pathway of mite allergen (Dermatophagoides pteronyassinus, Der p)‐induced nitric oxide (NO) production by AMs, and the role of SP‐D in the modulation of activated AMs by mite allergens. Methods Porcine SP‐D was purified from bronchoalveolar lavage fluids of Lan‐Yu mini‐pigs, by affinity chromatography on maltose‐sepharose. NO production, inducible expression of lipopolysaccharides (LPS)‐related binding and responding surface receptors complex, CD14 and toll‐like receptor 4 (TLR4), as well as inducible NO synthase (iNOs) and nuclear factor‐κB activation were studied in two AMs cell lines, MH‐S (BALB/c strain),and AMJ2‐C11 (C57BL/6 strain), and one peritoneal macrophage cell line (RAW264.7), after stimulation with LPS, or Der p. Results LPS and Der p elicited different responses of NO production in the different cell lines, and the response might depend upon the expression of the cell surface CD14/TLR4 complex in different genetic backgrounds of macrophage cell lines. Pretreatment of macrophages with SP‐D could inhibit NO production from Der p or LPS‐stimulated alveolar macrophages. Conclusion Mite allergen‐induced alveolar macrophage activation is mediated by CD14/TLR4 receptors and can be inhibited by SP‐D; it further supports the concept that SP‐D may be an important modulator of allergen‐induced pulmonary inflammation.