Inhibition of Mast Cell Degranulation by Surfactant Protein D

Abstract

Background: Surfactant protein D (SP-D) contributes to innate immunity within the lung and orchestrates cellular responses to pathogens and allergens. There have been suggestions that SP-D may inhibit allergen-induced mast cell activation through binding to allergens, but its actions on mast cells, or with other stimuli for degranulation have been little investigated. Aims: To determine the ability of SP-D to modulate mast cell degranulation, examining in particular substance P and calcium ionophore as stimuli. Methods: A recombinant fragment of SP-D was incubated with cells of the LAD2 mast cell line at various concentrations, and cells were stimulated with calcium ionophore or substance P. Degranulation was assessed by colourimetric determination of beta-hexosaminidase activity in cell supernatants. Results: SP-D inhibited substance P-induced beta-hexosaminidase release (P Conclusions: SP-D may contribute to lung homeostasis by suppressing mast cell activation. Degradation of SP-D as observed in the airways of asthmatics could may be a factor leading to increased mast cell activation.