Abstract
Infection with canine heartworm (Dirofilaria immitis), spread via mosquito vectors, causes coughing, asthma, pneumonia, and bronchitis in humans and other animals. The disease is especially severe and often fatal in dogs and represents a serious threat to public health worldwide. Cysteine protease inhibitors (CPIs), also known as cystatins, are major immunomodulators of the host immune response during nematode infections. Herein, we cloned and expressed the cystatin Di-CPI from D. immitis. Sequence analysis revealed two specific cystatin-like domains, a Q-x-V-x-G motif, and a SND motif. Phylogenetic analysis indicates that Di-CPI is a member of the second subgroup of nematode type II cystatins. Probing of D. immitis total proteins with anti-rDi-CPI polyclonal antibody revealed a weak signal, and immunofluorescence-based histochemical analysis showed that native Di-CPI is mainly localized in the cuticle of male and female worms and the gut of male worms. Treatment of canine peripheral blood mononuclear cells (PMBCs) with recombinant Di-CPI induced a Th2-type immune response characterized by high expression of the anti-inflammatory factor interleukin-10. Proliferation assays showed that Di-CPI inhibits the proliferation of canine PMBCs by 15%. Together, the results indicate that Di-CPI might be related to cellular hyporesponsiveness in dirofilariasis and may help D. immitis to evade the host immune system.
Highlights
The filarial nematode Dirofilaria immitis, known as canine heartworm, mainly occurs in tropical and temperate regions throughout the world, and causes canine and feline cardiopulmonary dirofilariasis as well as human pulmonary dirofilariasis [1]
The full-length Di-Cysteine protease inhibitors (CPIs) sequence was amplified from mixed-sex adult D. immitis cDNA samples and confirmed to be identical to the sequence obtained from the annotated D. immitis transcriptome [31]
Despite low overall sequence identity (20–30%) between Di-CPI and vertebrate type II cystatins (Mus musculus = 26%, Homo sapiens = 30%, Canis lupus familiaris = 25%), all the key structural features are conserved, including the conserved inhibitory domain signature Q-x-V-x-G associated with papain inhibition, the N-terminal glycine residue, the C-terminal PW motif, and a single disulfide bond
Summary
The filarial nematode Dirofilaria immitis, known as canine heartworm, mainly occurs in tropical and temperate regions throughout the world, and causes canine and feline cardiopulmonary dirofilariasis as well as human pulmonary dirofilariasis [1]. Dogs are the most suitable definitive host, which serves as a reservoir. As incidental hosts of D. immitis, Genes 2019, 10, 300; doi:10.3390/genes10040300 www.mdpi.com/journal/genes. Genes 2019, 10, 300 feline cardiopulmonary dirofilariasis and human pulmonary dirofilariasis are habitually misdiagnosed due to the asymptomatic nature of these diseases [1,5]. Given that D. immitis worms are continuously exposed to the host immune system, and yet can achieve a lifespan of years, they must engage in various immune evasion strategies [8]. During short-term immune evasion, infective larvae avoid host immune responses by releasing surface antigens, whereas in long-term immune evasion, pre-adult and adult worms mask their surface by adsorbing different host molecules and cells [9,10]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
