Immunoregulation within the granulomas of murine schistosomiasis mansoni

Neurokinin-1 receptor: functional significance in the immune system in reference to selected infections and inflammation

The G protein-coupled receptor (GPCR), neurokinin-1 receptor (NK1R), and its preferred ligand, substance P (SP), are reviewed in relationship to the immune system and selected infections. NK1R and SP are ubiquitous throughout the animal kingdom. This important pathway has unique functions in numerous cells and tissues. The interaction of SP with its preferred receptor, NK1R, leads to the activation of nuclear factor-kappa B (NF-κB) and proinflammatory cytokines. NK1R has two isoforms, both a full-length and a truncated form. These isoforms have different functional significances and differ in cell signaling capability. The proinflammatory signals modulated by SP are important in bacterial, viral, fungal, and parasitic diseases, as well as in immune system function. The SP-NK1R system is a major class 1, rhodopsin-like GPCR ligand-receptor interaction.

Schistosomiasis and liver fibrosis

Schistosoma mansoni infection invariably results in liver fibrosis of the host. This fibrosis may be represented by small focal areas of chronic inflammation and excess extracellular matrix deposited in periovular granulomas, distributed in variable numbers at the periphery of the portal vein system. This is the outcome of 90% of the infected population in endemic areas. Conversely, a minority of infected individuals develop extensive disease with numerous granulomas along the entire extension of the portal spaces. This latter situation is mainly dependent on special hemodynamic changes created by a heavy worm load, with the subsequent production of numerous eggs and represents a severe form of a peculiar chronic hepatopathy. Thus, host-parasite interactions in schistosomiasis help us to understand a number of important features of liver fibrosis: its initiation and regulation, the significance of accompanying vascular changes, the dynamics of fibrosis formation and regression with antiparasitic treatment; host genetic and immunological contributions, and the pathophysiology of portal hypertension.

Characterization of the Histoplasma capsulatum-induced granuloma

Rising rates of Histoplasma capsulatum infection are an emerging problem among the rapidly growing population of immune-compromised individuals. Although there is a growing understanding of systemic immunity against Histoplasma, little is known about the local granulomatous response, which is an important component in the control of infection. The focus of this article is the characterization of Histoplasma-induced granulomas. Five days after i.p. infection, infected macrophage appear in the liver and lung; however, no granulomas are apparent. Two days later, well-formed sarcoid granulomas are abundant in the lung and liver of infected mice, which contain all visible Histoplasma. Granulomas are dominated by macrophage and lymphocytes. Most of the Histoplasma and most of the apoptotic cells are found in the center of the lesions. We isolated liver granulomas at multiple time points after infection and analyzed the cellular composition, TCR gene usage, and cytokine production of granuloma-infiltrating cells. The lesions contain both CD4+ and CD8+ T cell subsets, and T cells are the primary source of IFN-gamma and IL-17. The main source of local TNF-alpha is macrophage. Chemokines are produced by both infiltrating macrophage and lymphocytes. Dendritic cells are present in granulomas; however, T cell expansion seems to occur systemically because TCR usage is very heterogeneous even at the level of individual lesions. This study is the first direct examination of host cellular responses in the Histoplasma-induced granuloma representing the specific interface between host and pathogen. Our studies will allow further analysis of key elements of host Histoplasma interactions at the site of chronic infection.

PD-L2+ dendritic cells and PD-1+ CD4+ T cells in schistosomiasis correlate with morbidity

Dendritic cells (DC) are critical antigen-presenting cells for the induction and control of immune responses. PD-L2 (B7-DC) is a regulatory ligand on subpopulations of DC, and binds to the co-regulatory receptor PD-1, present on some activated T lymphocytes, leading to down-regulation. We now show that very early during experimental schistosomiasis (by 5 weeks) a significantly higher proportion of splenic CD11c+/B220- DC express PD-L2, and by 6 weeks after infection a higher proportion of splenic CD4 T cells express PD-1. In this CBA/J mouse/Schistosoma mansoni chronic infection model we have shown that most mice develop moderate morbidity (Moderate Splenomegaly Syndrome, MSS), while some parallel-infected mice express different immune characteristics and die or develop severe morbidity (Hypersplenomegaly Syndrome, HSS). We now report a positive correlation between the proportion of splenic CD11c+/B220- DC that express PD-L2 and showing MSS. In contrast, there is an inverse correlation between the proportion of splenic CD3+/CD4+ T lymphocytes that express PD-1 and showing MSS. The data demonstrate that schistosomes can induce sustained elevated percentages of PD-L2-expressing, B220-negative DC. Furthermore, when this potentially immunoregulatory environment occurs chronically, infected mice are most likely to have developed MSS, expressing moderate morbidity.

Immunoregulation and World Health Assembly resolution 54.19: why does treatment control morbidity?

World Health Assembly resolution 54.19, passed in May, 2001, declares the intent of the World Health Organization member States to implement a combined strategy for the control of morbidity caused by schistosomiasis and soil-transmitted helminths. Among other things, the resolution urges ministries to treat all clinical cases and groups at high risk of morbidity such as children, women and those exposed occupationally. The policy is predicated on the evidence that morbidity due to these infections can be controlled by periodic treatment with appropriate chemotherapeutic, anti-helminthic drugs. While it is true that annual or biannual praziquantel treatment for schistosomiasis decreases morbidity, we now question how treatment leads to this beneficial effect. It is clear that treatment kills worms, but we propose that this is only a part of how it leads to reduced morbidity in areas of ongoing transmission and reinfection. By killing worms, we postulate that treatment also effects immunologic changes to the normal host/parasite relationship, and the resulting immune responses lead to both increased resistance (protection against reinfection), and increased immunoregulatory mechanisms that control morbidity upon subsequent reinfections. If the effects of treatment contribute to morbidity control in these ways, a better understanding of how this occurs may allow optimization of these effects of treatment through appropriate periodic treatment regimens, resulting in less reinfection and better morbidity control when reinfection does occur.

HIV infection and tropical parasitic diseases - deleterious interactions in both directions?

HIV and parasitic infections interact and affect each other mutually. Whereas HIV infection may alter the natural history of parasitic diseases, impede rapid diagnosis or reduce the efficacy of antiparasitic treatment, parasitoses may facilitate the infection with HIV as well as the progression from asymptomatic infection to AIDS. We review data on known interactions for malaria, leishmaniasis, Human African Trypanosomiasis, Chagas' disease, onchocerciasis, lymphatic filariasis, schistosomiasis and intestinal helminthiases. The common immunopathogenetic basis for the deleterious effects parasitic diseases may have on the natural history of HIV infection seems to be a particular type of chronic immune activation and a preferential activation of the T helper (Th)2 type of help. Control of parasitic diseases should complement the tools currently used in combating the HIV pandemic.

Female genital schistosomiasis: facts and hypotheses

In this paper we summarise the parasitological, clinical and epidemiological characteristics of female genital schistosomiasis (FGS), a frequent manifestation of the infection with Schistosoma haematobium. Means to diagnose and treat lesions in the lower and upper genital tract are discussed. Based on clinical findings and available pathophysiological as well as immunological data it is conceivable that FGS of the cervix and vagina not only facilitates the infection with agents of sexually transmitted diseases, but presumably also alters the natural history of such infections. Two infectious agents are of particular concern: the Human Immunodeficiency Virus and the oncogenic Human Papilloma Viruses. Possible interactions and their consequences are discussed and research areas which should be addressed are outlined.

The Substance P Receptor Is Necessary for a Normal Granulomatous Response in Murine Schistosomiasis Mansoni

Immune cells within the granulomas of murine schistosomiasis mansoni make the neuropeptide substance P (SP) and express neurokine 1 receptor, which is the specific receptor for substance P (SPr). It was determined if mice with deletion of the SPr (SPr−/−) would develop a normal granulomatous response to schistosome ova during the course of natural infection. Mean liver granuloma size was smaller in SPr−/− mice compared with that of wild-type control animals. Although flow analysis revealed little difference in the cellular composition of the granulomas, both splenocytes and granuloma cells from SPr−/− mice produced much less IFN-γ and IgG2a and less IgE. The expression of Th2 cytokines (IL-4/IL-5) and IgG1 was comparable to the wild-type control. The mouse with targeted disruption of its SPr had the nonmammalian gene encoding the enzyme β-galactosidase inserted in exon 1 of the SPr gene. There was β-galactosidase activity in many mononuclear cells scattered throughout the schistosome granulomas of SPr−/− mice. Also, a granuloma T cell line derived from this transgenic mouse produced β-galactosidase. These results provide further evidence that in murine schistosomiasis SPr is displayed commonly on granuloma inflammatory cells and is important for granuloma development and expression of IFN-γ circuitry in this natural infection.