Ticks are important ectoparasites and vectors of multiple human and animal diseases. The obligatory hemophagy of ticks provides a formidable route for parasite transmission from one host to another. Parasite survival inside the tick relies on the ability of a pathogen to escape or inhibit tick immune defenses, but the molecular interactions between the tick and its pathogens remain poorly understood. Here we report that tick genomes are unique in that they contain all known classes of the α(2)-macroglobulin family (α(2)M-F) proteins: α(2)-macroglobulin pan-protease inhibitors, C3 complement components, and insect thioester-containing and macroglobulin-related proteins. By using RNA interference-mediated gene silencing in the hard tick Ixodes ricinus we demonstrated the central role of a C3-like molecule in the phagocytosis of bacteria and revealed nonredundant functions for α(2)M-F proteins. Assessment of α(2)M-F functions in a single organism should significantly contribute to the general knowledge on the evolution and function of the complement system. Importantly, understanding the tick immune mechanisms should provide new concepts for efficient transmission blocking of tick-borne diseases.
- MeSH
- alpha-Macroglobulins genetics MeSH
- Chryseobacterium immunology pathogenicity MeSH
- Phagocytosis genetics MeSH
- Genome immunology MeSH
- Genomics MeSH
- Hemocytes immunology metabolism microbiology pathology MeSH
- Insect Proteins genetics metabolism MeSH
- Flavobacteriaceae Infections genetics immunology MeSH
- Complement C3 genetics metabolism MeSH
- Cells, Cultured MeSH
- Humans MeSH
- RNA, Small Interfering genetics MeSH
- Evolution, Molecular MeSH
- Sequence Analysis, DNA MeSH
- Animals MeSH
- Check Tag
- Humans MeSH
- Animals MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
The universal protease inhibitors of the alpha(2)-macroglobulin (alpha(2)M) family are evolutionarily conserved constituents of innate immunity, presumably because they guard organisms against undesired proteolytic attacks of a different origin. Here, we determined the primary structure of alpha(2)-macroglobulin from the hard tick Ixodes ricinus (IrAM) by sequencing of overlapping PCR products. Predicted disulfide and glycosylation patterns, post-translational cleavage and alternative splicing within its 'bait region' demonstrate that IrAM is closely related to the alpha(2)-macroglobulin from the soft tick Ornithodoros moubata. The IrAM message is expressed in all tick developmental stages and tissues, except for the gut, and the protein was detected to be mainly present in the hemolymph. Silencing of IrAM by dsRNA interference markedly reduced the phagocytosis of a potential pathogen, Chryseobacterium indologenes, by tick hemocytes both in vitro and in vivo. In contrast, phagocytosis of the Lyme disease spirochete Borrelia burgdorferi or a commensal bacteria Staphylococcus xylosus was not affected by the IrAM knock-down. Similar results were obtained upon deactivation of all thioester proteins in tick hemolymph by methylamine. We have further demonstrated that phagocytosis of C. indologenes is dependent on an active metalloprotease secreted by the bacteria. These data indicate that interaction of tick alpha(2)-macroglobulin with a protease of an invading pathogen is linked with cellular immune response.
- MeSH
- alpha-Macroglobulins pharmacology genetics chemistry immunology MeSH
- Chryseobacterium immunology MeSH
- Phagocytosis immunology MeSH
- Phenanthrolines pharmacology MeSH
- Financing, Organized MeSH
- Hemocytes immunology microbiology drug effects MeSH
- Hemolymph immunology MeSH
- Ixodes genetics immunology microbiology MeSH
- Metalloproteases metabolism drug effects MeSH
- Methylamines pharmacology MeSH
- Molecular Sequence Data MeSH
- RNA Interference MeSH
- Amino Acid Sequence MeSH
- Base Sequence MeSH
- Sequence Alignment MeSH
- Animals MeSH
- Check Tag
- Animals MeSH
