Hodžić A, Mateos-Hernández L, Leschnik M, Alberdi P, Rego ROM, et al.
Vaccines •
Due to the functional inactivation of the gene encoding for the enzyme that is involved in the oligosaccharide galactose-α-1,3-galactose (α-Gal) synthesis, humans and Old-World primates are able to produce a large amount of antibodies against the glycan epitope. Apart from being involved in the hyperacute organ rejection in humans, anti-α-Gal antibodies have shown a protective effect against some pathogenic agents and an implication in the recently recognized tick-induced mammalian meat allergy. Conversely, non-primate mammals, including dogs, have the ability to synthetize α-Gal and, thus, their immune system is not expected to naturally generate the antibodies toward this self-antigen molecule. However, in the current study, we detected specific IgG, IgM, and IgE antibodies to α-Gal in sera of clinically healthy dogs by an indirect enzyme-linked immunosorbent assay (ELISA) for the first time. Furthermore, in a tick infestation experiment, we showed that bites of induce the immune response to α-Gal in dogs and that the resulting antibodies (IgM) might be protective against . These findings may help lead to a better understanding of the underlying mechanisms involved in mammalian meat allergy and tick-host-pathogen interactions, but they also open up the question about the possibility that dogs could develop an allergy to mammalian meat after tick bites, similar to that in humans.
The carbohydrate Galα1-3Galβ1-(3)4GlcNAc-R (α-Gal) is produced in all mammals except for humans, apes and old world monkeys that lost the ability to synthetize this carbohydrate. Therefore, humans can produce high antibody titers against α-Gal. Anti-α-Gal IgE antibodies have been associated with tick-induced allergy (i.e. α-Gal syndrome) and anti-α-Gal IgG/IgM antibodies may be involved in protection against malaria, leishmaniasis and Chagas disease. The α-Gal on tick salivary proteins plays an important role in the etiology of the α-Gal syndrome. However, whether ticks are able to produce endogenous α-Gal remains currently unknown. In this study, the Ixodes scapularis genome was searched for galactosyltransferases and three genes were identified as potentially involved in the synthesis of α-Gal. Heterologous gene expression in α-Gal-negative cells and gene knockdown in ticks confirmed that these genes were involved in α-Gal synthesis and are essential for tick feeding. Furthermore, these genes were shown to play an important role in tick-pathogen interactions. Results suggested that tick cells increased α-Gal levels in response to Anaplasma phagocytophilum infection to control bacterial infection. These results provided the molecular basis of endogenous α-Gal production in ticks and suggested that tick galactosyltransferases are involved in vector development, tick-pathogen interactions and possibly the etiology of α-Gal syndrome in humans.
Galectin-4 and its homologue galectin-6 are members of the tandem-repeat subfamily of monomer divalent galectins. Expression of mouse galectin-4 and galectin-6 by RT-PCR using primers designed to distinguish both galectin transcripts indicates that both are expressed in the small intestine, colon, liver, kidney, spleen and heart and P19X1 cells while only galectin-4 is expressed in BW-5147 and 3T3 cell lines. In situ hybridization confirmed the presence of galectin-4/-6 transcripts in the liver and small intestine. Galectin-4 is expressed in spermatozoons and oocytes and its expression during early mouse emryogenesis appears in 8-cell embryos and remains in later stages, as tested by RT-PCR. To study the role of carbohydrate recognition domains (CRDs) in oligosaccharide binding and epitope recognition, we cloned mouse full-length galectin-4 and galectin-6 cDNA and constructed bacterial expression vectors producing histidin-tagged recombinant galectin-4 and its truncated CRD1 and CRD2 forms. Oligosaccharide binding profile for all recombinant forms was assessed using Glycan Array available through the Consortium for Functional Glycomics. Acquired data indicate that mGalectin-4 binds to alpha-GalNAc and alpha-Gal A and B type structures with or without fucose. While the CRD2 domain has a high specificity and affinity for A type-2 alpha-GalNAc structures, the CRD1 domain has a broader specificity in correlation to the total binding profile. These data suggest that CRD2 might be the dominant binding domain of mouse galectin-4. Mapping of epitopes reactive for biotinylated his-tagged CRD1, CRD2 and mGalectin-4 performed on mouse cryosections showed that all three forms bind to alveolar macrophages, macrophages of red pulp of the spleen and proximal tubuli of the kidney and this binding was inhibited by 5 mM lactose. Interestingly, mGalectin-4, but not CRD forms, binds to the suprabasal layer of squamous epithelium of the tongue, suggesting that the link region also plays an important role in ligand recognition.
