Differential expression of anti-glycan antibodies in schistosome-infected humans, rhesus monkeys and mice

Abstract

Schistosomiasis is a debilitating parasitic disease of humans, endemic in tropical areas, for which no vaccine is available. Evidence points to glycan antigens as being important in immune responses to infection. Here we describe our studies on the comparative humoral immune responses to defined schistosome-type glycan epitopes in Schistosoma mansoni-infected humans, rhesus monkeys and mice. Rhesus anti-glycan responses over the course of infection were screened on a defined glycan microarray comprising semi-synthetic glycopeptides terminating with schistosome-associated or control mammalian-type glycan epitopes, as well as a defined glycan microarray of mammalian-type glycans representing over 400 glycan structures. Infected rhesus monkeys generated a high immunoglobulin G (IgG) antibody response to the core xylose/core α3 fucose epitope of N-glycans, which peaked at 8-11 weeks post infection, coinciding with maximal ability to kill schistosomula in vitro. By contrast, infected humans generated low antibody levels to this epitope. At 18 months following praziquantel therapy to eliminate the parasite, antibody levels were negligible. Mice chronically infected with S. mansoni generated high levels of anti-fucosylated LacdiNAc (GalNAcβ1, 4(Fucα1, 3)GlcNAc) IgM antibodies, but lacked a robust response to the core xylose/core α3 fucose N-glycan antigens compared with other species studied, and their sera demonstrated an intermediate level of schistosomula killing in vitro. These differential responses to parasite glycan antigens may be related to the ability of rhesus monkeys to self-cure in contrast to the chronic infection seen in humans and mice. Our results validate defined glycan microarrays as a useful technology to evaluate diagnostic and vaccine antigens for schistosomiasis and perhaps other infections.

Identification of Antigenic Glycans from Schistosoma mansoni by Using a Shotgun Egg Glycan Microarray

“…3B), primarily to fractions F7 to F13, but only during the patent period at 8 weeks postinfection. No significant antibody response to these glycans was obtained with the serum of animals infected for 78 weeks in either this study or a recent one from our group (24). The results suggest that anti-glycan responses to some antigens dissipate by this stage of the infection in rhesus monkeys.…”

“…PNGase A can release N-glycans containing unusual core modifications that block PNGase F release. It is possible that the cleavage of glycans with PNGase A results in an alteration in the conformation of antigenic features within the glycan cores that are recognized by antibodies, especially in light of results from Luyai et al that demonstrated that rhesus and human sera strongly recognized core ␣3-fucosylated and core ␤2-xylosylated glycans when presented as glycopeptides on a defined glycan microarray, implying the need for a peptide moiety in the recognition (24). The glycan microarrays we prepared here from SEA were developed by reductive amination with AEAB and free glycans; thus, they lack a peptide component.…”

“…Complex type Nglycans possessing core ␣3-fucose and core ␤2-xylose, associated with resistance to PNGase F but not PNGase A, have been detected in schistosomes (27-29, 31, 41, 49, 67). Smit et al (31) showed that the core ␣3-fucosylated egg N-glycans were primarily complex, in contrast to the truncated trimannose used on the defined array in Luyai et al (24), to which a robust rhesus response was seen. Therefore, the low reactivity of rhesus antibodies with our PNGase A-released fractions could be explained by a preference for truncated rather than complex core ␣3 fucosylated N-glycans, which may be expressed earlier than the egg stage.…”

“…Interestingly, monoclonal antibodies (MAbs) specific to these glycans recognize these antigens on the surface of 3-h-old schistosomula, and some anti-glycan antibodies can mediate killing in vitro in a complement-dependent fashion (18)(19)(20)(21). Schistosoma mansoniinfected rhesus monkeys, which are known to self-cure after infection, have IgG to many glycan antigens, including Le x , LDN, LDNF, core fucose, and core xylose determinants, and their sera are effective in complement-mediated cytolysis of cells expressing Le x as well as schistosomulum larvae in vitro (22)(23)(24). However, it is unknown whether anti-glycan antibodies contribute to parasite killing by animal sera in vivo.…”

“…The combination of these techniques, i.e., glycomics and/or glycan structural profiling, which is guided by the use of immunologically relevant reagents, such as antisera and MAbs, has great potential to improve our understanding of the anti-glycan response and uncover novel, immunologically relevant diagnostic and vaccine candidates. We recently found that there were both similarities and substantial differences in the specificity, titers, and isotype composition of anti-glycan antibodies among rhesus monkeys (naturally protected hosts) as well as humans and mice (chronically infected hosts) based on a small collection of semisynthetic, schistosome-type biantennary N-glycans (24). In the present study, utilizing methods for fluorescent covalent tagging, separation, and printing of glycans (35,36), we generated a natural N-glycan microarray from S. mansoni egg glycoproteins.…”