Soluble intercellular adhesion molecules in human schistosomiasis: correlations with disease severity and decreased responsiveness to egg antigens

Schistosome Egg Migration: Mechanisms, Pathogenesis and Host Immune Responses

Many parasitic worms possess complex and intriguing life cycles, and schistosomes are no exception. To exit the human body and progress to their successive snail host, Schistosoma mansoni eggs must migrate from the mesenteric vessels, across the intestinal wall and into the feces. This process is complex and not always successful. A vast proportion of eggs fail to leave their definite host, instead becoming lodged within intestinal or hepatic tissue, where they can evoke potentially life-threatening pathology. Thus, to maximize the likelihood of successful egg passage whilst minimizing host pathology, intriguing egg exit strategies have evolved. Notably, schistosomes actively exert counter-inflammatory influences on the host immune system, discreetly compromise endothelial and epithelial barriers, and modulate granuloma formation around transiting eggs, which is instrumental to their migration. In this review, we discuss new developments in our understanding of schistosome egg migration, with an emphasis on S. mansoni and the intestine, and outline the host-parasite interactions that are thought to make this process possible. In addition, we explore the potential immune implications of egg penetration and discuss the long-term consequences for the host of unsuccessful egg transit, such as fibrosis, co-infection and cancer development.

Schistosoma "Eggs-Iting" the Host: Granuloma Formation and Egg Excretion

Schistosomiasis is a major cause of morbidity in humans invoked by chronic infection with parasitic trematodes of the genus Schistosoma. Schistosomes have a complex life-cycle involving infections of an aquatic snail intermediate host and a definitive mammalian host. In humans, adult male and female worms lie within the vasculature. Here, they propagate and eggs are laid. These eggs must then be released from the host to continue the life cycle. Schistosoma mansoni and Schistosoma japonicum reside in the mesenteric circulation of the intestines with egg excreted in the feces. In contrast, S. haematobium are present in the venus plexus of the bladder, expelling eggs in the urine. In an impressive case of exploitation of the host immune system, this process of Schistosome “eggs-iting” the host is immune dependent. In this article, we review the formation of the egg granuloma and explore how S. mansoni eggs laid in vasculature must usurp immunity to induce regulated inflammation, to facilitate extravasation through the intestinal wall and to be expelled in the feces. We highlight the roles of immune cell populations, stromal factors, and egg secretions in the process of egg excretion to provide a comprehensive overview of the current state of knowledge regarding a vastly unexplored mechanism.

Cardiovascular disease detection using bio-sensing techniques

Universally, cardiovascular disease (CVD) is recognised as the prime cause of death with estimates exceeding 20 million by 2015 due to heart disease and stroke. Facts regarding the disease, its classification and diagnosis are still lacking. Hence, understanding the issues involved in its initiation, its symptoms and early detection will reduce the high risk of sudden death associated with it. Biosensors developed to be used as rapid screening tools to detect disease biomarkers at the earliest stage and able to classify the condition are revolutionising CVD diagnosis and prognosis. Advances in interdisciplinary research areas have made biosensors faster, highly accurate, portable and environmentally friendly diagnostic devices. The recent advances in microfluidics and the advent of nanotechnology have resulted in the development of improved diagnostics through reduction of analysis time and integration of several clinical assays into a single, portable device as lab-on-a-chip (LOC). The development of such affinity based systems is a major drive of the rapidly growing nanotechnology industry which involves a multidisciplinary research effort encompassing nanofluidics, microelectronics and analytical chemistry. This review summarised the classification of CVD, the biomarkers used for its diagnosis, biosensors and their application including the latest developments in the field of heart-disease detection.

Eosinophilia and thrombosis in parasitic diseases: an overview

It is known that peripheral blood eosinophilia (PBE) is a normal hematopoietic response to several parasitic diseases, but it is less known that PBE promotes a hypercoagulable state that may favor thrombosis. Scope of this article is to explore which parasitic infestations are most likely to be complicated by thrombosis and to highlight the pathogenetic contribution of PBE to vascular occlusions in this setting. A review of the world literature revealed 18 cases in which PBE was associated with vascular occlusion though no specific surveys were dedicated to this topic. The eosinophil exerts its thrombogenic potential by inhibition of the natural anticoagulant pathways and release of tissue factor with enhanced coagulation activation leading to vascular occlusion. It is hoped that this review contributes to the awareness of the link between PBE and thrombosis in parasitic disorders to foster research in this area.

sTNFR-II and sICAM-1 are associated with acute disease and hepatic inflammation in schistosomiasis japonica

Soluble intracellular adhesive molecule 1 (sICAM-1) and tumour necrosis factor receptors I (TNFR-1) and II (TNFR-II) have been shown to be associated with numerous liver disorders. Shedding of these membrane proteins can be triggered by the Th1 cytokines, TNF-alpha and IFN-gamma, which are associated with susceptibility or resistance to hepatic schistosomiasis, respectively. Further, TNF-alpha receptors and sICAM-1 have been implicated in periportal fibrosis in advanced human schistosomiasis mansoni and correlate with schistosome granuloma formation in the murine model. We measured serum levels of sICAM-1, TNFR-I and TNFR-II in Chinese patients with different clinically defined stages of schistosomiasis japonica and controls; these included 35 patients with acute schistosomiasis, 45 patients with chronic schistosome infections, 34 advanced patients with evidence of severe morbidity and 20 patients with no known history of exposure to infection. Markedly elevated levels of soluble TNFRs (sTNFRs) and sICAM-1 were observed in the acute and advanced patients compared with the chronic and control groups. Mean sTNFR-II levels were significantly higher in acute patients compared with advanced (P < 0.00001) and chronic patients (P < 0.00001) and showed the strongest association of the markers with acute disease (odds ratio (OR) = 1.099). sTNFR-II and sICAM-1 levels both correlated with infection intensity and there were significant positive correlations observed between eosinophil count and infection intensity (P = 0.0072) and sICAM-1 (P = 0.0014). Although there were significantly higher levels of antigen-specific IgG4 and total IgG in infected individuals compared with controls, none correlated with infection intensity. Further, no differences in IgG4 and total IgG levels were observed between the acute and chronic groups. The results suggest sTNFRs and sICAM-1 are associated with liver inflammation and disease progression. Measurement of sTNFR-II and sICAM-1 levels in serum could serve as additional markers for the diagnosis of acute stage disease and the monitoring of hepatic inflammation in human schistosomiasis japonica.

Soluble cellular adhesion molecules, selectins, VEGF and endothelin-1 in patients with Wuchereria bancrofti infection and association with clinical status

Lymphatic filariasis, a mosquito-transmitted disease commonly known as Bancroftian filariasis, is characterized by debilitating pathology linked to the progression of lymphoedema to a chronic state of elephantiasis. We performed longitudinal measurements of endothelial adhesion and angiogenic molecules in 63 Polynesian patients living in an hyperendemic focus of Wuchereria bancrofti. Decreased serum concentrations of soluble (s-) L selectin (CD62L) were noticed in sera of of patients with chronic conditions (hydrocele and elephantiasis). Chyluria was associated with increased vascular endothelial growth factor (VEGF) levels, whereas elephantiasis presented a high endothelin-1 (ET-1) profile. By contrast, increased serum concentrations of soluble intercellular (sICAM-1, CD54), but not of vascular cell (sVCAM-1, CD106), adhesion molecules were observed in sera of patients with bacterial lymphangitis used as controls. These trends are consistent with the increased permeability of vascular structures, a major clinical feature observed in acute lymphatic pathology (of bacterial or filarial origin), and of fundamental differences in the pathogenesis of hydrocele and elephantiasis. Using markers correlated with the clinical status (high ET-1 and VEGF levels for elephantiasis and chyluria, respectively; low CD62L levels for hydrocoele and elephantiasis) it should be possible to monitor disease progression in lymphatic filariasis.

Schistosome glycoconjugates in host-parasite interplay

Schistosomes are digenetic trematodes which cause schistosomiasis, also known as bilharzia, one of the main parasitic infections in man. In tropical and subtropical areas an estimated 200 million people are infected and suffer from the debilitating effects of this chronic disease. Schistosomes live in the blood vessels and strongly modulate the immune response of their host to be able to survive the hostile environment that they are exposed to. It has become increasingly clear that glycoconjugates of schistosome larvae, adult worms and eggs play an important role in the evasion mechanisms that schistosomes utilise to withstand the immunological measures of the host. Upon infection, the host mounts innate as well as adaptive immune responses to antigenic glycan elements, setting the immunological scene characteristic for schistosomiasis. In this review we summarise the structural data now available on schistosome glycans and provide data and ideas regarding the role that these glycans play in the various aspects of the glycobiology and immunology of schistosomiasis.

Systemic modulation of peripheral eosinophilia (air pouch model) in Schistosoma mansoni infection

Schistosoma mansoni infection induces in their hosts a marked and sustained eosinophilia, which is influenced or modulated by complex mechanisms, that vary according to the phase of infection. To address this phenomenon, we used the air pouch (AP) model in control and infected Swiss webster mice, analyzing the cellular, tissue response and local expression of adhesion molecules [CD18 (beta(2)-chain), CD44, ICAm-1 (CD54), L-selectin (CD62L), CD49d (alpha(4)-chain), LFA1 (CD11 alpha)]. Infected animals were studied at 3 (pre-oviposition phase), 7 (acute phase), and 14 (chronic phase) weeks after infection (5-6 mice/period of infection). Normal mice were age-matched. Results showed that after egg stimulation, compared with matched controls, the infected mice, at each point of infection, showed a lower eosinophil response in the acute (7 weeks) and chronic phase (14 weeks) of infection. However, when the infected mice were in pre-oviposition phase (3 weeks) their eosinophil response surpassed the control ones. In the AP wall of infected mice, a significant decrease in the expression of ICAM-1 and CD44 in fibroblastic-like cells and a reduction in the number of CD18 and CD11 alpha in migratory cells were observed. The other adhesion molecules were negative or weakly expressed. The results indicated that in the air pouch model, in S. mansoni-infected mice: (1) eosinophil response is strikingly down-regulated, during the acute ovular phase; (2) in the pre-oviposition phase, in contrast, it occurs an up-regulatory modulation of eosinophil response, in which the mechanisms are completely unknown; (3) in the chronic phase of the infection, the down modulation of eosinophil response is less pronounced; 4) Down-regulation of adhesion molecules, specially of ICAM-1 appear to be associated with the lower eosinophil response.

Serum concentrations of sICAM-1, sE-, sP- and sL-selectins in patients with Schistosoma mansoni infection and association with disease severity

Increased serum concentrations of soluble intercellular adhesion molecule-1 (sICAM-1, CD54) and of soluble E- (CD62E), but not soluble P- (CD62P) and L- (CD62 L) selectins, were detected in Malagasy patients living in an hyperendemic focus of Schistosoma mansoni. Levels of sICAM-1 remained elevated for several months after treatment with praziquantel. Serum levels of ICAM-1, but not of other markers, were significantly correlated with the disease severity, as indicated by ultrasonographical data, and with some circulating fibrosis markers (at least hyaluronic acid). sICAM-1 level may reflect endothelial inflammatory reactions, probably harmful, in the liver and may be useful for monitoring morbidity evolution in schistosomiasis mansoni.

High Levels of TNF, Soluble TNF Receptors, Soluble ICAM-1, and IFN-γ, but Low Levels of IL-5, Are Associated with Hepatosplenic Disease in Human Schistosomiasis Mansoni

In a case-control study based in two areas of Kenya, hepatosplenic schistosomiasis mansoni was shown to be linked with low levels of IL-5 and with correspondingly high IFN-γ, TNF, and circulating soluble TNF receptor I (sTNFR-I), sTNFR-II, and sICAM-1. PBMC from the hepatosplenic cases responded to in vitro Ag stimulation with significantly higher levels of IFN-γ and TNF, but lower levels of IL-5, compared with nonhepatosplenic controls matched for age and infection intensity. Most of these correlations were confounded by differences between geographical areas. However, principle component analysis identified a high IFN-γ and TNF, and low IL-5 axis in the data as the first principle component; this was significantly associated with hepatosplenomegaly (p &lt; 0.0005) even after controlling for area. High plasma levels of sTNFR-I (p &lt; 0.001), sTNFR-II, (p &lt; 0.0001), and sICAM-1 (p &lt; 0.009) were also significantly associated with hepatosplenomegaly, independently of area, in the case of the soluble forms of both TNF receptors. These parameters were negatively related to IL-5. These results suggest that proinflammatory cytokines are involved in the hepatosplenic disease process in infected individuals who have low anti-inflammatory Th2 responses and that sTNFR may be a useful circulating marker for this disease process, perhaps reflecting the level of TNF activity in hepatic tissues.

Intercellular adhesion molecule 1 is the major adhesion molecule expressed during schistosome granuloma formation

Endothelial cell adhesion molecules play a key role in inflammation by initiating leukocyte trafficking. One of the most complex inflammatory responses is the formation of a cellular granuloma. Expression of adhesion molecules during granuloma formation was investigated by using the murine host reaction to schistosome parasite eggs deposited in the liver as a model. By both immunohistochemistry and lymphocyte adhesion assays, the predominant interaction identified was between intercellular adhesion molecule 1 (ICAM-1) and its cognate integrin, leukocyte functional antigen 1 (LFA-1). ICAM-1 expression on sinusoidal endothelium was induced when eggs were first deposited in the liver, peaked in parallel with granuloma size, and was downregulated with modulation of the granuloma. Polyacrylamide beads coated with soluble parasite egg antigens could induce ICAM-1 expression on endothelial cells in vitro only in the presence of tumor necrosis factor alpha, a cytokine previously shown to be key to granuloma formation. A role for ICAM-1 in recruiting lymphocytes to the hepatic granuloma was also supported by the observation that lymphocytes preincubated with anti-LFA-1 antibody did not bind to granulomas in tissue sections. While ICAM-1 is the predominant adhesion molecule in schistosome egg granuloma formation in wild-type mice, when the ICAM-1 gene is knocked out, vascular cell adhesion molecule 1 is upregulated and granuloma formation is preserved.

In situ analysis of B7-2 costimulatory, major histocompatibility complex class II, and adhesion molecule expression in schistosomal egg granulomas

Immunopathological damage in schistosomiasis consist of egg granuloma formation, which is a hypersensitivity reaction mediated by antigen-specific CD4+ T helper (Th) lymphocytes. Th cells are dependent on accessory cell-bound co-stimulatory signals for activation. The B7 molecules provide critical costimulation, as in their absence T cells are rendered unresponsive. We investigated the kinetics of B7-2 molecule expression in schistosomal egg granulomas by immunocytochemical analysis in situ. We also monitored major histocompatibility complex (MHC) class II, intercellular adhesion molecule 1 (ICAM-1) and vascular cell adhesion molecule 1 (VCAM-1) expression, as well as the presence of macrophages, T cells, and B cells. B7-2 expression was elevated in cells of the large granulomas of the acute (6-1/2 week) infection, and sharply declined thereafter. MHC class II expression was similarly elevated in the acute granulomas, but in contrast to B7-2, remained relatively constant throughout 12 1/2 weeks of infection. Moreover, ICAM-1 and VCAM-1 were expressed in acute and chronic granulomas. However, whereas ICAM-1 was constitutively expressed in normal liver, VCAM-1 was dramatically induced in the livers upon onset of disease. The findings suggest that the acute granulomas are rich in accessory cells with overall phenotypic configurations that support Th-cell activation, although at subsequent times, granulomas contain increasing numbers of B7-poor accessory cells capable of inducing Th-cell unresponsiveness. Thus, cellular interactions in early granulomas may be able to amplify egg-induced immunopathology, whereas interactions taking place in succeeding granulomas appear to precipitate its down-regulation.

T-lymphocyte responsiveness in murine schistosomiasis mansoni is dependent upon the adhesion molecules intercellular adhesion molecule-1, lymphocyte function-associated antigen-1, and very late antigen-4

Granuloma formation in murine schistosomiasis is dependent on CD4+ Th lymphocytes and requires recruitment and accumulation of inflammatory cells at the site of egg deposition. The present study examined the role of three adhesion molecules, intercellular adhesion molecule-1 (ICAM-1), lymphocyte function-associated antigen-1 (LFA-1), and very late antigen-4 (VLA-4), that participate in cellular recruitment, interaction, and lymphocyte activation during in vitro activation of acutely and chronically infected spleen and liver granuloma lymphocytes. Blockade of ICAM-1, LFA-1, or VLA-4 by rat monoclonal antibody inhibited spleen and granuloma lymphocyte interleukin-2 (IL-2) and IL-4 production as well as lymphoproliferative responses at similar levels (66 to 87%). The down-modulated cytokine and proliferative responses of chronically infected lymphocytes were inhibited to the same extent as their acutely infected counterparts. Cell sorting analysis demonstrated that acutely and chronically infected splenic and granuloma lymphocytes expressed similar levels of LFA-1, ICAM-1, and VLA-4 and that more ICAM-1 was expressed on infected than on uninfected mouse lymphocytes. By exposure of cells to paired monoclonal antibodies at suboptimal doses, it was determined that whereas all three adhesion molecules may participate, only ICAM-1 and LFA-1 showed synergistic interactions in determining lymphocyte responsiveness. These data suggest that spleen and liver granuloma lymphocytes are equally well armed with functional adhesion receptors. Thus, ICAM-1, LFA-1, and VLA-4 play an important accessory role in inflammatory cytokine production and lymphocyte proliferation, and therefore these adhesion molecules may participate in the initiation and maintenance of the granulomatous inflammation.

Immune response of mice infected with Schistosoma mansoni is modulated by antifibrotic treatment

Mice infected with Schistosoma mansoni treated with beta-aminopropionitrile (BAPN), an antifibrotic agent, and the antischistosomal drug praziquantel (PZQ) were resistant to challenge for up to 5 weeks post-treatment. The combined treatment resulted in profound changes to the liver granuloma cell matrix and the composition and function of the cellular infiltrate. Although granulocytes always predominated in the infiltrate, the proportion of the cells which were macrophages was higher in mice treated with BAPN alone (39.2%) than in infected mice which were untreated (15.2%) or treated with PZQ alone (12.4%), and much higher than in mice given the combined treatment (1.8%). Two products associated with macrophage activation and cytotoxicity [tumour necrosis factor-alpha (TNF-alpha) and nitric oxide] were only detected in mice harbouring a patent infection and there was a strong positive correlation between the concentrations of each. The relatively low TNF-alpha concentrations in BAPN-treated mice seemed to be associated with the relatively small granulomas observed in these mice. BAPN treatment also led to changes in the proliferative response of the treated mice's macrophages to mitogen and soluble schistosome-egg antigen and in spleen cellularity; these changes are probably associated with the resistance to challenge infection observed in mice given BAPN with PZQ. It is clear that BAPN treatment changes the dynamics of the delayed-type hypersensitivity response within the granuloma and that this impacts on other immunological sites. How this relates to the maintenance of post-treatment resistance to a challenge infection has still to be elucidated.