Novel expression of a functional trimeric fragment of human SP-A with efficacy in neutralisation of RSV

作者：Watson Alastair; Kronqvist Nina; Spalluto C Mirella; Griffiths Mark; Staples Karl J; Wilkinson Tom; Holmskov Uffe; Sorensen Grith L; Rising Anna; Johansson Jan; Madsen Jens; Clark Howard

来源：Immunobiology, 2017, 222(2): 111-118.

DOI：10.1016/j.imbio.2016.10.015

• Surfactant protein A
• Recombinant trimeric fragment
• Respiratory syncytial virus
• NT domain
• Innate immunity
• Neutralisation
• Collectin

Respiratory syncytial virus (RSV) is the leading cause of bronchiolitis and hospitalisation of infants in developed countries. Surfactant protein A (SP-A) is an important innate immune molecule, localized in pulmonary surfactant. SP-A binds to carbohydrates on the surface of pathogens in a calcium-dependent manner to enable neutralisation, agglutination and clearance of pathogens including RSV.
SP-A forms trimeric units and further oligomerises through interactions between its N-terminal domains. Whilst a recombinant trimeric fragment of the closely related molecule (surfactant protein D) has been shown to retain many of the native protein's functions, the importance of the SP-A oligomeric structure in its interaction with RSV has not been determined.
The aim of this study was to produce a functional trimeric recombinant fragment of human (rfh)SP-A, which lacks the N-terminal domain (and the capacity to oligomerise) and test its ability to neutralise RSV in an in vitro model of human bronchial epithelial infection.
We used a novel expression tag derived from spider silk proteins ('NT') to produce rfhSP-A in Escherichia coli, which we found to be trimeric and to bind to mannan in a calcium-dependent manner. Trimeric rfhSP-A reduced infection levels of human bronchial epithelial (AALEB) cells by RSV by up to a mean (+/- SD) of 96.4 (+/- 1.9) % at 5 mu g/ml, which was significantly more effective than dimeric rfhSP-A (34.3 (+/- 20.5) %) (p<0.0001). Comparatively, native human SP-A reduced RSV infection by up to 38.5 (+/- 28.4) %.
For the first time we report the development of a functional trimeric rfhSP-A molecule which is highly efficacious in neutralising RSV, despite lacking the N-terminal domain and capacity to oligomerise.

• 出版日期2017-2