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A frequently observed feature of active infection with filarial nematodes is the presence of lymphocytes in the bloodstream that have impaired responsiveness to antigen. It is generally accepted that such a defect in lymphocyte function could contribute to the failure of the immune system to eliminate filarial nematodes. For this reason, understanding the mechanism underlying lymphocyte 'hyporesponsiveness' is an important goal for immunologists who study filarial nematodes. Thus, although there has long been an interest in answering questions such as what stage(s) of the nematode causes hyporesponsiveness, more recently, lymphocyte hyporesponsiveness has been increasingly studied at the molecular level. The result of this is that we are now beginning to learn much of the nature and cause of phenotypic changes in the hyporesponsive lymphocyte and also of the identity of the nematode-derived molecules that induce them. As this information continues to be generated, the challenge will be to use it to find a way of reversing lymphocyte hyporesponsiveness in the hope that this will lead to rejection of filarial nematodes in the parasitized human host.

ES-62 is a phosphorylcholine-containing glycoprotein secreted by filarial nematodes. This molecule has been shown to reduce the severity of inflammation in collagen-induced arthritis (CIA) in mice, a model of rheumatoid arthritis, via down-regulation of anti-collagen type 1 immune responses. Malaria parasites induce a pro-inflammatory host immune response and many of the symptoms of malaria are immune system-mediated. Therefore we have asked whether the immunomodulatory properties of ES-62 can down-regulate the severity of malaria infection in BALB/c mice infected with Plasmodium chabaudi. We have found that ES-62 has no significant effect on the course of P. chabaudi parasitaemia, and does not significantly affect any of the measures of malaria-induced pathology taken throughout infection.

SUMMARY Modulation of macrophage/dendritic cell (DC) cytokine production by the filarial nematode phosphorylcholine (PC)-containing product, ES-62, is mediated by Toll-like receptor (TLR) 4 and signal transduction depends on the TLR adaptor MyD88. Intriguingly, comparison of TLR4 knock-out (ko) mice with TLR4 mutant C3H/HeJ mice indicates that ES-62 cytokine responses are not dependent on the Pro712 residue of TLR4, which is crucial for the response to bacterial lipopolysaccharide (LPS). Because other immunomodulatory effects of ES-62 have been attributed to PC we have now investigated, using PC conjugated to ovalbumin (PC-Ova), whether PC is responsible for the interaction of ES-62 with TLR4. PC-Ova mimicked the modulation of interleukin (IL)-12 production by ES-62 in a TLR4- and MyD88-dependent manner and as with native ES-62, PC-Ova effects were not dependent on Pro712. Furthermore, both native ES-62 and PC-Ova suppressed Akt phosphorylation, whereas neither altered the activation of p38 or Erk MAP kinases. To rule out any role for the ES-62 protein component, we tested a PC-free recombinant ES-62 (rES-62) generated in the yeast Pichia pastoris. Surprisingly, rES-62 also modulated IL-12 production, but in a TLR4/MyD88-independent manner. Furthermore, rES-62 strongly activated both the p38 and Erk MAP kinases and Akt. However, recent biophysical analysis suggests there are differences in folding/shape between native and rES-62 and hence data obtained with the latter should be treated with caution. Nevertheless, although our study indicates that PC is likely to be primarily responsible for the modulation of cytokine production observed with native ES-62, an immunomodulatory role for the protein component cannot be ruled out.

Long-term infection with parasitic worms is generally associated with an immunological phenotype that is Th2-like and anti-inflammatory. This phenotype is probably an unintentional consequence of molecular characteristics of worms (as free-living worms also express polarising molecules) in combination with deliberate attempts by the parasites, via molecular secretions, to modulate the phenotype. This review is concerned with the identity of immunomodulatory worm products, the receptors that they interact with and the signal transduction pathways that they activate. It hopes to indicate how knowledge of these factors can explain the changes in gene expression that result in the characteristic worm-induced immunological phenotype.

1. The 'hygiene hypothesis' postulates that the recent increased incidence of allergic or autoimmune diseases (e.g. asthma, type I diabetes) in the West reflects an absence of appropriate priming of the immune response by infectious agents, such as parasitic worms, during childhood. 2. Consistent with this, it has long been recognized that several autoimmune disorders, such as rheumatoid arthritis (RA), a T helper (Th) 1-mediated autoimmune disease characterized by excess production of pro-inflammatory cytokines, such as tumour necrosis factor-alpha, exhibit reduced incidence and severity in geographical regions with high parasite load, suggesting that environmental factors may subtly alter disease progression. 3. Infection with worms also appears to suppress Th2-biased inflammatory disorders, such as asthma, because there also appears to be an inverse correlation between parasite load and atopy. This is perhaps more surprising, given that helminths often induce strong Th2-type immune responses characterized by release of specific cytokines, such as interleukin (IL)-4, IL-5 and IL-13. 4. Therefore, these findings suggest that the co-evolution of helminths with hosts, which has resulted in the ability of worms to modulate inflammatory responses in order to promote parasite survival, may also have generated a predisposition for the host to develop autoimmunity and allergy in the absence of infection. 5. The mechanisms underlying such immunomodulation are not clear, but appear to involve the release of parasite-derived molecules that allow the worms to modulate or evade the host immune response by a number of mechanisms, including skewing of cytokine responses and the induction of T regulatory cells. 6. In the present review we discuss the properties of one such filarial nematode-derived immunomodulatory molecule, namely ES-62, its anti-inflammatory action and the therapeutic potential of small molecule derivatives and peptides that mimic its action.

ES-62 is a phosphorylcholine (PC)-containing glycoprotein secreted by filarial nematodes, parasites of vertebrates including humans. We have previously demonstrated that pre-exposure to this molecule in vitro interferes with subsequent B-cell receptor (BCR)-dependent activation of murine splenic B lymphocytes. To investigate the significance of this during filarial nematode infection, we now employ mice exposed to ES-62, at concentrations equivalent to those found for PC-containing molecules in the bloodstream of parasitized humans, via release from implanted osmotic pumps. Using this approach, we reveal that splenic and lymph node mononuclear cells, and also purified splenic B cells recovered from these mice have reduced ability ex vivo to proliferate in response to BCR ligation. The effect on BCR-induced proliferation was further investigated with respect to elucidating the mechanism of action of the parasite product and was shown to be associated with impaired signal transduction affecting the ErkMAPkinase pathway. Also, it was found that ES-62 did not act by promoting apoptosis or by priming for apoptosis following subsequent stimulation, but rather, appeared to render cells hyporesponsive to stimulation. ES-62 is thus shown for the first time to be a potent modulator of B lymphocyte function in vivo at a concentration relevant to natural filarial nematode infection. This finding considerably strengthens the idea that ES-62 plays a role in evasion of the immune response during parasitism.

SUMMARY Immunomodulatory properties of phosphorylcholine (PC)-containing glycosphingolipids from Ascaris suum were investigated utilizing immune cells from BALB/c mice. Proliferation of splenic B cells induced either via F(ab′)2 fragments of anti-murine Ig (anti-Ig) or LPS was significantly reduced when the glycosphingolipids were present in the culture medium. However whereas the LPS-mediated effect was dependent on the PC moiety of the glycosphingolipids, the result generated when using anti-Ig was not. Analysis of cell cycle status and mitochondrial potential indicated that the combination of the glycosphingolipids and anti-Ig reduced B cell proliferation, at least in part, by inducing apoptosis. Consistent with the observed suppression of B cell activation/cell cycle progression, investigation of the effect of glycosphingolipid pre-exposure on mitogenic B cell signal transduction pathways activated by anti-Ig, revealed a PC-independent inhibitory effect on dual (thr/tyr) phosphorylation and activation of ErkMAPKinase. The glycosphingolipids were also investigated for their inhibitory effect on LPS/IFN-γ induced Th1/pro-inflammatory cytokine production by peritoneal macrophages. It was found that IL-12 p40 production was inhibited and in an apparently PC-dependent manner. Overall these data indicate that PC-containing glycosphingolipids of A. suum appear to have at least two immunomodulatory constituents – PC and an as yet unknown component.

Obesity, one of the main causes of metabolic syndrome (MetS), is an increasingly common health and economic problem worldwide, and one of the major risk factors for developing type 2 diabetes and cardiovascular disease. Chronic, low-grade inflammation is associated with MetS and obesity. A dominant type 2/anti-inflammatory response is required for metabolic homoeostasis within adipose tissue: during obesity, this response is replaced by infiltrating, inflammatory macrophages and T cells. Helminths and certain protozoan parasites are able to manipulate the host immune response towards a TH2 immune phenotype that is beneficial for their survival, and there is emerging data that there is an inverse correlation between the incidence of MetS and helminth infections, suggesting that, as with autoimmune and allergic diseases, helminths may play a protective role against MetS disease. Within this review, we will focus primarily on the excretory-secretory products that the parasites produce to modulate the immune system and discuss their potential use as therapeutics against MetS and its associated pathologies.