Evaluation of the role of galectins in parasite immunity

Reducing fecal egg count through selective breeding alters dorper lamb response to Haemonchus contortus in an artificial challenge trial

Infection by gastrointestinal nematodes (GIN), particularly Haemonchus contortus, can be detrimental to sheep health and performance. Genetic susceptibility to GIN varies between breeds, with those lacking high levels of natural resistance often requiring frequent anthelmintic treatment when facing parasitic challenge. Genetic technology can serve as a tool to decrease GIN susceptibility via selection for sheep with reduced fecal egg count (FEC) estimated breeding values (EBVs). However, the physiological changes that result from implementation of this strategy are not well described. Additionally, there is a need for comparison of animals from recent selective breeding against breeds with inherent GIN resistance. In this study we administered a challenge of H. contortus to Dorper x White Dorper (DWD; n = 92) lambs that have been genetically selected for either low (DWD-) or high (DWD+) FEC EBVs and Barbados Blackbelly x Mouflon (BBM; n = 19) lambs from a genetically resistant breed backgrounds. Lamb FEC, packed-cell volume (PCV) and serum IgG were measured at intermittent levels over 5 weeks. At day 21 and day 35, the selectively bred DWD- had a lower mean FEC compared to DWD+, but were higher than BBM. Reductions in both PCV and serum IgG from initial day 0 levels were observed in DWD lambs, but not in BBM. Furthermore, from a subset of lambs (n = 24) harvested at day 21, DWD- only tended (p = 0.056) to have lower mean worm counts than DWD+, with BBM having the lowest mean worm count. Differentially expressed genes (DEGs) identified via RNA-sequencing of abomasal tissue at day 21 indicate a more pronounced Th2 immune response and more rapid worm expulsion occurred in iBBM than iDWD- and iDWD+ lambs. However, gene expression in DWD- suggests an association between reduced FEC EBV and gastric acid secretion and the ability to limit worm fecundity. Ultimately, selection of Dorper sheep for low FEC EBV can reduce susceptibility to GIN, but it will likely require multiple generations with this trait as a breeding priority before presenting a similar resistance level to Caribbean breeds.

Galectins in Protozoan Parasitic Diseases: Potential Applications in Diagnostics and Therapeutics

Neglected tropical diseases (NTDs) constitute a group of diseases that generally develop in tropical or subtropical climatic conditions and are related to poverty. Within the spectrum of NTDs, diseases caused by protozoa such as malaria, Chagas disease, and leishmaniasis exhibit elevated mortality rates, thereby constituting a substantial public health concern. Beyond their protozoan etiology, these NTDs share other similarities, such as the challenge of control and the lack of affordable, safe, and effective drugs. In view of the above, the need to explore novel diagnostic predictors and therapeutic targets for the treatment of these parasitic diseases is evident. In this context, galectins are attractive because they are a set of lectins bound to β-galactosides that play key roles in a variety of cellular processes, including host-parasite interaction such as adhesion and entry of parasites into the host cells, and participate in antiparasitic immunity in either a stimulatory or inhibitory manner, especially the galectins-1, -2, -3, and -9. These functions bestow upon galectins significant therapeutic prospects in the context of managing and diagnosing NTDs. Thus, the present review aims to elucidate the potential role of galectins in the diagnosis and treatment of malaria, leishmaniasis, and Chagas disease.

Enhanced mucosal response in sheep harbouring βA beta-globin against haemonchosis

Association between ovine β-globin polymorphisms and resistance against haemonchosis was described and related to the mechanism of high oxygen affinity βA ➔ βC switch during anaemia, but there are no studies regarding the involved local host responses. Phenotypic parameters and local responses were evaluated in sheep from two β-globin haplotypes naturally infected with Haemonchus contortus. Morada Nova lambs were monitored at 63, 84 and 105 days of age for faecal egg counts and packed cell volume (PCV) under natural infection with H. contortus. At 210 days of age, lambs of Hb-AA and Hb-BB β-globin haplotypes were euthanised, and the fundic region of abomasum was sampled for evaluation of microscopic lesions and relative expression of genes related to immune, mucin and lectin activities. Lambs harbouring the βA allele presented an improved resistance/resilience against clinical haemonchosis, showing higher PCV during infection. Hb-AA animals presented increased eosinophilia in the abomasum compared to Hb-BB animals, accompanied by higher Th2 profile, mucin and lectin activity transcripts, while the inflammatory response was increased in Hb-BB animals. This is the first report to demonstrate an enhanced local response in the primary site of H. contortus infection related to βA allele of β-globin haplotype.

In vitro culture of parasitic stages of Haemonchus contortus

Haemonchus contortus is a constraint to sheep production. Seeking to reduce the use of hosts and produce parasitic stages in large-scale, a 42-day in vitro culture protocol of H. contortus third-stage larvae was optimized using Dulbecco's modified Eagle's medium (DMEM). In cell-free culture, larvae were maintained at 39.6°C, in acidic media (pH 6.1) for 3 or 6 days with Δ4-dafachronic acid followed by DMEM pH 7.4 supplemented or not with Fildes' reagent. In DMEM pH 7.4 at 37°C, supplementation with Caco-2 cells was compared to Fildes. On Day 14, fourth-stage larvae (L4) development rates in acidic media supplemented (86.8-88.4%) or not (74.4-77.8%) with Fildes and in Caco-2 cell co-culture (92.6%) were similar, and superior to DMEM pH 7.4 with Fildes (0.0%). On Day 21, Caco-2 cell co-culture resulted in higher larvae differentiation (25.0%) and lower degeneration (13.9%) compared to acidic media (1.5-8.1% and 48.6-69.9%, respectively). This is the first report of prolonged in vitro culture of H. contortus larvae using commercial media in co-culture with Caco-2 cells. Although no progression to the adult stage, Caco-2 cell co-culture resulted in morphological differentiation of H. contortus L4 and larval viability for up to 28 days.

The oligomeric assembly of galectin-11 is critical for anti-parasitic activity in sheep (Ovis aries)

Galectins are a family of glycan-binding molecules with a characteristic affinity for ß-D-glycosides that mediate a variety of important cellular functions, including immune and inflammatory responses. Galectin-11 (LGALS-11) has been recently identified as a mediator induced specifically in animals against gastrointestinal nematodes and can interfere with parasite growth and development. Here, we report that at least two natural genetic variants of LGALS-11 exist in sheep, and demonstrate fundamental differences in anti-parasitic activity, correlated with their ability to dimerise. This study improves our understanding of the role of galectins in the host immune and inflammatory responses against parasitic nematodes and provides a basis for genetic studies toward selective breeding of animals for resistance to parasites.

Brugia malayi galectin 2 is a tandem-repeat type galectin capable of binding mammalian polysaccharides

Galectins are among the most abundant excretory/secretory (ES) products of filarial worms, but their role in filarial biology is poorly understood. Galectin-2 (Lec-2), a major component of Brugia malayi extracellular vesicles, is released by filarial worms, and was recently identified in the serum of persons with loiasis. We therefore sought to clone and characterize Lec-2, and to develop reagents to examine its potential as a biomarker and its role in parasite biology. We cloned and expressed recombinant B. malayi Lec-2 (rBmLec-2), generated a Lec-2-specific monoclonal antibody (4B4), and used it to confirm the presence of Lec-2 in B. malayi ES products and whole worm lysate. We show that Lec-2 is absent in B. malayi oocytes, and increases in concentration as embryos mature. Recombinant BmLec-2 hemagglutinates rabbit red blood cells at concentrations less than 1 μg/mL, and this is abrogated by single amino acid substitutions in the predicted carbohydrate recognition domains. rBmLec-2 binds multiple LacNAc oligosaccharides on a mammalian carbohydrate array. Sera from 17/23 (78 %) persons with microfilaremic loiasis and 4/10 (40 %) persons with bancroftian filariasis had detectable antibody to Lec-2 by western blot. Our studies confirm the functionality of BmLec-2 and indicate anti-Lec-2 antibody responses are common in persons with filariasis. These studies set the stage for further examination of the role of Lec-2 in filarial biology and in filarial-host interactions.

The roles of galectins in parasitic infections

Galectins is a family of multifunctional lectins. Fifteen galectins have been identified from a variety of cells and tissues of vertebrates and invertebrates. Galectins have been shown to play pivotal roles in host-pathogen interaction such as adhesion of pathogens to host cells and activation of host innate and adaptive immunity. In recent years, the roles of galectins during parasite infections have gained increasing attention. Galectins produced by different hosts can act as pattern recognition receptors detecting conserved pathogen-associated molecular patterns of parasites, while galectins produced by parasites can modulate host responses. This review summarizes some recent studies on the roles of galectins produced by parasitic protozoa, nematodes, and trematodes and their hosts. Understanding the roles of galectins in host-parasite interactions may provide targets for immune intervention and therapies of parasitic infections.