Abstract
Surfactant proteins (SPs)-A and -D are C-type lectins of the collectin family and function in the clearance of infectious particles in the lungs. Some polymorphisms of SPs that give rise to amino acid changes have been found to affect their function. Several SP-A gene polymorphisms have been reported to be associated with respiratory infection diseases, such as tuberculosis (TB). However, the relationship between surfactant proteins D (SP-D) polymorphisms and TB is still unclear. To study the associations between SP-D polymorphisms and TB, the correlations of SP-D polymorphisms with TB were examined in a case–control study, which included 364 patients with TB and 177 control subjects. In addition, we cloned two major SP-D exonic polymorphism C92T (rs721917) and A538G (rs2243639) constructs and used these for in vitro assays. The effects of SP-D polymorphisms on agglutination and other interactions with Mycobacterium bovis bacillus Calmette–Guérin (M. bovis BCG) were evaluated. In comparison with SP-D 92C (amino acid residue 16, Threonine), our results showed that SP-D 92T (amino acid residue 16, Methionine) had a lower binding ability to M. bovis BCG, a lower capacity to inhibit phagocytosis, lesser aggregation, poorer survival of bacillus Calmette–Guérin (BCG)-infected MH-S cells, and less inhibition of intracellular growth of M. bovis BCG. The case–control association study showed that the 92T homozygous genotype was a risk factor for TB. However, a lesser effect was seen for polymorphism A538G. In conclusion, the results of functional and genetic analyses of SP-D variants consistently showed that the SP-D 92T variant increased susceptibility to TB, which further confirmed the role of SP-D in pulmonary innate immunity against mycobacterial infection.
Highlights
Pulmonary tuberculosis (TB), caused by Mycobacterium tuberculosis (MTB), is a global public health issue, as it is the leading cause of death among infectious diseases in many countries
We examined the roles of the four variants of Recombinant surfactant proteins D (SP-D) (rSP-D) in the binding to M. bovis bacillus Calmette–Guérin (BCG)
Surfactant proteins D genetic polymorphisms are most often associated with pulmonary diseases, and our hypostatized genetic variants of SP-D may have different levels of contribution to the pathogenesis of TB
Summary
Pulmonary tuberculosis (TB), caused by Mycobacterium tuberculosis (MTB), is a global public health issue, as it is the leading cause of death among infectious diseases in many countries. The development of and susceptibi lity to TB involves complicated host environment–pathogen interactions, and genetic components have been suggested to be involved in the process. Data accumulated from different types of studies, such as twin studies [5, 6], genome-wide linkage analyses [7,8,9,10], and genome-wide association studies [11,12,13], have demonstrated that individuals with particular genetic variations are at high risk of TB [14]. Among people infected with TB, only 10% develop active pulmonary TB, implying that polymorphisms of genes associated with host immune responses may be key to the development of pulmonary TB [15]
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