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Correspondence |

Serum Surfactant Protein D as a Marker of Asthma Severity FREE TO VIEW

Alida Benfante, MD; Salvatore Battaglia, MD; Nicola Scichilone, MD
Author and Funding Information

FINANCIAL/NONFINANCIAL DISCLOSURES: None declared.

aDipartimento Biomedico di Medicina Interna e Specialistica, Sezione di Pneumologia, Università degli Studi di Palermo, Palermo, Italy

bIstituto Euro-Mediterraneo di Scienza e Tecnologia (IEMEST), Palermo, Italy

CORRESPONDENCE TO: Nicola Scichilone, MD, Dipartimento di Biomedicina e Medicina Specialistica, Sezione di Pneumologia, University of Palermo, Palermo, Italy, via Trabucco 180, 90146 Palermo, Italy.


Copyright 2016, American College of Chest Physicians. All Rights Reserved.


Chest. 2016;150(2):473-474. doi:10.1016/j.chest.2016.05.032
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We have read with great interest the article by Mackay et al published in CHEST (May 2016) entitled “Airway Surfactant Protein D Deficiency in Adults with Severe Asthma.” As elegantly shown, serum surfactant protein D (SP-D) concentrations were significantly lower in individuals with severe asthma as opposed to individuals with mild asthma and healthy control subjects, and SP-D levels were significantly higher in the BAL of patients with severe asthma compared with those with mild asthma. On this basis, the authors propose that serum SP-D could serve as a biomarker of the most severe forms of asthma. In their article, Mackay et al state that “To the best of our knowledge, this study is the first to investigate the relationship between asthma and SP-D concentration in patients with such severe disease.” We respectfully disagree with this statement, since we recently reported that indeed serum SP-D concentrations are significantly higher in individuals with severe asthma as opposed to healthy control subjects and individuals with mild asthma, and their levels correlate with the degree of airway obstruction. In our study, we hypothesized that serum SP-D could increase as a result of inflammation-induced permeability of the bronchial microvasculature, which allows the passage of large macromolecules, such as hydrophilic surfactant proteins, from lung to blood. However, the increased levels of surfactant proteins in serum could also be explained by an increased local synthesis of surfactant proteins induced by local inflammation.

SP-D contributes to pathogen clearance and resolution of inflammation as a component of the innate immune defense within the airway. In this context, Mackay et al propose that the degradation of SP-D would render the airways susceptible to airway infections, thus leading to frequent exacerbations and features of treatment-resistant asthma. To complement the immunologic role, surfactant also acts by stabilizing the conducting airways. In this scenario, the increased surface tension caused by the loss of the surfactant function would oppose the bronchodilatory ability of deep inspirations, which has been demonstrated to decrease with the severity of asthma. The effectiveness of the beneficial effects of lung inflation on airways is dependent on the interdependence between the parenchyma that surrounds and sustains the small airways and the outer airway walls. This is further supported by the significant relationship between serum SP-D levels and functional abnormalities of small airways. We believe that the findings of the two studies could provide a potential explanation to the pathophysiological mechanisms of severe asthma.

References

Mackay R.M. .Grainge C.L. .Lau L.C. .Barber C. .Clark H.W. .Howarth P.H. . Airway surfactant protein D deficiency in adults with severe asthma. Chest. 2016;149:1165-1172 [PubMed]journal. [CrossRef] [PubMed]
 
Benfante A. .Battaglia S. .Principe S. .et al Asthmatics with high levels of serum surfactant protein D have more severe disease. Eur Respir J. 2016;47:1864-1867 [PubMed]journal. [CrossRef] [PubMed]
 
Folkesson H.G. .Westrom B.R. .Pierzynowski S.G. .Karlsson B.W. . Lung to blood passage of different-sized molecules during lung inflammation in the rat. J Appl Physiol. 1991;71:1106-1111 [PubMed]journal. [PubMed]
 
Xu J. .Singhera G. .Dorsheid D.R. . Expression of surfactant protein D in airways of asthmatics and interleukin-13 modulation of surfactant protein D in human models of airway epithelium. Respir Res. 2015;16:26- [PubMed]journal. [CrossRef] [PubMed]
 
Scichilone N. .Marchese R. .Soresi S. .Interrante A. .Togias A. .Bellia V. . Deep inspiration-induced changes in lung volume decrease with severity of asthma. Respir Med. 2007;101:951-956 [PubMed]journal. [CrossRef] [PubMed]
 

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References

Mackay R.M. .Grainge C.L. .Lau L.C. .Barber C. .Clark H.W. .Howarth P.H. . Airway surfactant protein D deficiency in adults with severe asthma. Chest. 2016;149:1165-1172 [PubMed]journal. [CrossRef] [PubMed]
 
Benfante A. .Battaglia S. .Principe S. .et al Asthmatics with high levels of serum surfactant protein D have more severe disease. Eur Respir J. 2016;47:1864-1867 [PubMed]journal. [CrossRef] [PubMed]
 
Folkesson H.G. .Westrom B.R. .Pierzynowski S.G. .Karlsson B.W. . Lung to blood passage of different-sized molecules during lung inflammation in the rat. J Appl Physiol. 1991;71:1106-1111 [PubMed]journal. [PubMed]
 
Xu J. .Singhera G. .Dorsheid D.R. . Expression of surfactant protein D in airways of asthmatics and interleukin-13 modulation of surfactant protein D in human models of airway epithelium. Respir Res. 2015;16:26- [PubMed]journal. [CrossRef] [PubMed]
 
Scichilone N. .Marchese R. .Soresi S. .Interrante A. .Togias A. .Bellia V. . Deep inspiration-induced changes in lung volume decrease with severity of asthma. Respir Med. 2007;101:951-956 [PubMed]journal. [CrossRef] [PubMed]
 
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