A 6-year-old child with vacant episodes and unilateral convulsions

Regulating immunity to malaria

The optimal outcome of a malaria infection is that parasitized cells are killed and degraded without inducing significant pathology. Since much of the pathology of malaria infection can be immune-mediated, this implies that immune responses have to be carefully regulated. The mechanisms by which anti-malarial immune responses are believed to be regulated were discussed at the recent Malaria Immunology Workshop (Bloomberg School of Public Health, Johns Hopkins University, Baltimore, Maryland, USA; February 2005). Potential regulatory mechanisms include regulatory T cells, which have been shown to significantly modify cellular immune responses to various protozoan infections, including leishmania and malaria; neutralising antibodies to pro-inflammatory malarial toxins such as glycosylphosphatidylinositol and haemozoin; and self-regulating networks of effector molecules. Innate and adaptive immune responses are further moderated by the broader immunological environment, which is influenced by both the genetic background of the host and by co-infection with other pathogens. A detailed understanding of the interplay between these different immunoregulatory processes may facilitate the rationale design of vaccines and novel therapeutics.

Fulminant Hepatic Failure from Herpes Simplex Virus: Post Liver Transplantation Acyclovir Therapy and Literature Review

INTRODUCTION

Herpes simplex virus (HSV) is seen throughout the world and can be treated with acyclovir. We present a case of fulminant hepatic failure (FHF) as a result of disseminated HSV infection in a pregnant patient during the second trimester.

METHODS

The medical records of a patient suffering from HSV-related fulminant hepatic failure were collected. A review of the literature was collected and reported.

RESULTS

A previously healthy female presented with fulminant hepatic failure at a local emergency room complaining of a 5-day history of fever, nausea, vomiting, and right side abdominal pain that radiated to the back. She was diagnosed with fulminant hepatic failure and progressed into a coma. The patient underwent orthotopic liver transplantation (OLT) prior to the diagnosis of HSV and then treated successfully with acyclovir.

CONCLUSION

Treatment of HSV fulminant hepatitis is dependent up on early suspicion and prompt intervention. In addition, antiviral therapy may need to be lifelong.

Age-dependent effect of plasma nitric oxide on parasite density in Ghanaian children with severe malaria

Nitric oxide (NO) has toxic properties against Plasmodium falciparum. While high blood levels have been associated with protection against severe malarial disease, they may also contribute to the pathophysiology of cerebral malaria and severe anaemia. Promoter variants in the inducible nitric oxide synthase (iNOS) gene have been shown to influence NO concentrations and disease manifestation. However, findings are conflicting. We examined associations of plasma NO metabolites (NOx) with symptoms of severe malaria, particularly malarial anaemia and cerebral malaria, and with iNOS promoter variants. In 210 Ghanaian children with severe malaria, we measured plasma nitrite, nitrate, and S-nitrosothiol, and genotyped the iNOS promoter variants -954G-->C, -1173C-->T, and the -2.5 kb (CCTTT)(n) microsatellite. NOx levels decreased with age. In young children (<24 months), high NOx was associated with reduced parasite density. This was not seen in patients of 24-48 months of age and reversed in older children. Subgroup analysis revealed that in children with severe anaemia but without cerebral involvement (prostration, impaired consciousness, convulsions), high NOx levels correlated with low parasitaemia (P = 0.02). In these children, elevated NOx levels were also associated with the iNOS-954C-->T/(CCTTT)(8) haplotype (P = 0.03). No association between NOx or iNOS genotypes and cerebral malaria was observed. Our findings suggest that in young children with severe malaria NOx reduces parasitaemia. This effect wanes at higher ages and may reflect a predominance of unspecific immune responses to infection in early childhood. This finding may have importance for the understanding of associations between iNOS variants and severe malaria in regions of differing disease manifestation.

iNOS promoter variants and severe malaria in Ghanaian children

Nitric oxide is an important mediator in the host defence against Plasmodium falciparum malaria. It has antiparasitic effects in vitro. However, its role in clinical disease remains controversial. Polymorphisms in the inducible nitric oxide synthase promoter (iNOS; -954G-->C, -1173C-->T, -2.6 kb CCTTT(n) microsatellite) may influence susceptibility to and severity of malaria. We tested this hypothesis in a case-control study among Ghanaian children with severe malaria (SM) and asymptomatic parasitaemia, respectively, and in healthy controls. In this study, the respective frequencies of iNOS-954G-->C and -1173C-->T did not differ between groups but > or =13 microsatellite copies were associated with SM. -954G-->C and -1173C-->T were in linkage disequilibrium with CCTTT(8) and CCTTT(13), respectively. -954G-->C/CCTTT(8) protected against hyperparasitaemia whereas -1173C-->T/CCTTT(13) increased fatality. These findings suggest that iNOS promoter haplotypes rather than single nucleotide polymorphisms are associated with malaria in Ghanaian children.

Limits of early diagnosis of herpes simplex encephalitis in children: a retrospective study of 38 cases

The prognosis of herpes simplex encephalitis (HSE) depends on the early and appropriate administration of specific antiviral therapy. We retrospectively reviewed 38 cases of children with proven HSE, to evaluate the reliability of polymerase chain reaction results, according to the time of cerebrospinal fluid (CSF) sampling. Initial negative results were observed in 8 of 33 CSF samples drawn before day 3 of the disease and were significantly associated with a low level of protein and <10 leukocytes/mm3 in the CSF.

Nucleotide and haplotypic diversity of the NOS2A promoter region and its relationship to cerebral malaria

To assess the hypothesis that nitric oxide is critical in the pathogenesis of cerebral malaria, we analysed genetic variation in the proximal promoter region of NOS2A, the gene encoding inducible nitric oxide synthase. Sequencing 72 Gambian chromosomes revealed 11 single nucleotide polymorphisms in 2.5 kB (theta=8.6 x 10(-4)). Genotyping 104 nuclear families identified six common haplotypes. A single haplotype, uniquely defined by the NOS2A-1659T allele, was associated with cerebral malaria by a transmission disequilibrium test of 334 affected children and their parents (P=0.02). An independent case-control study of 505 different children from the same population replicated the allelic association with cerebral malaria (odds ratio: 1.31, P=0.04). Taken together these data indicate a weak but significant association of the NOS2A locus with susceptibility to cerebral malaria. Despite high linkage disequilibrium across the region studied, this association would not have been detected without the initial construction of a dense marker set for haplotype tagging.

Inducible and endothelial constitutive nitric oxide synthase gene polymorphisms in Kawasaki disease

BACKGROUND

Nitric oxide (NO) is secreted by immune and vascular endothelial cells, and appears to play important roles in the pathophysiology of Kawasaki disease (KD). Thus, genetic variations in NO synthase (NOS) genes may be involved in the development of coronary artery lesions (CAL) in KD.

METHODS

The present study investigated the association of endothelial constitutive NOS (ecNOS) and inducible NOS (iNOS) gene polymorphisms with the development of CAL in KD in a Japanese population.

RESULTS

The genotype distributions of 27-bp tandem repeat polymorphism within intron 4 of ecNOS gene did not show any significant difference between controls and KD patients with or without CAL. In addition, there was no significant association between whole-allele distribution of iNOS gene promoter (penta-repeat CCTTT) polymorphism and KD with or without CAL.

CONCLUSION

These results did not support any association of ecNOS and iNOS gene polymorphisms to the development of CAL in KD patients in a Japanese population.

The molecular epidemiology of malaria

This review discusses how the use of molecular genetic techniques such as the polymerase chain reaction are helping in the management and prevention of malaria.

Expression of inducible nitric oxide synthase (iNOS) mRNA in target organs of lethal and non-lethal strains of murine malaria

Nitric oxide (NO) is a putative mediator of the immunological and/or pathological responses to malaria, consequently it is a potential target for novel drug therapy. Numerous cell types increase expression of inducible nitric oxide synthase (iNOS) under inflammatory conditions, the most relevant stimuli being cytokines and endotoxins. In this study the expression of iNOS mRNA in several target organs (brain, liver, spleen) of malaria have been investigated in MF1 mice during lethal Plasmodium (P.) berghei and non-lethal P. c. chabaudi infection. In P. berghei malaria, iNOS mRNA decreased in liver and was unchanged in spleen during the period of rising parasitaemia, but increased in both organs late in the infection, when parasitaemia was high and death imminent. In mice infected with P. c. chabaudi, spleen iNOS mRNA increased progressively throughout the early, peak and recovery periods of parasitaemia, but decreased in liver. Brain iNOS mRNA decreased in samples collected throughout the time courses of both infections. Hence it is evident that changes in iNOS mRNA in murine malaria depend upon the tissue, day of infection, degree of parasitaemia and strain of Plasmodium. These data indicate induction of iNOS mRNA in the spleen has a role in combating these strains of Plasmodium in MF1 mice. Failure to clear lethal P. berghei parasitaemia was associated with increased iNOS mRNA expression in the liver, which may contribute to the pathology of this malaria.

Cerebral malaria and immunogenetics

Cerebral malaria depends largely on the capacity of Plasmodium falciparum infected red blood cells to adhere to the endothelia of microvessels, leading to their occlusion. The most important players include receptors expressed on the surface of the endothelial cell and known to interact with the parasite, cytokines modulating the expression of these adhesion molecules and nitric oxide (NO). Platelets, monocytes and lymphocytes have the ability to adhere to these endothelial receptors and to one another, leading to a more complex situation and an increase in the degree of vessel occlusion. The polymorphism of all these molecules, implicated either in adhesion, in modulation of this adhesion or activation of the expression of diverse endothelial mediators should be an important field of study. Polymorphism of five of these molecules has been explored so far: ICAM-1, TNF-alpha, IL-1-beta, inducible NOS and complement receptor-1 (CR-1). To these studies can be added those concerning mannose binding protein (MBP), a protein playing a role in innate immunity, and the class-I antigen HLA-B53. To date, the only clear cut result concerns TNF-alpha. With the other polymorphisms, either no association is found (IL-1RA, CR-1, MBP), or the results are geographically heterogeneous (ICAM-1, HLA-B53), or contradictory (iNOS2). Most often, the candidate gene approach has been followed, as part of case control studies. One of the main problems in this approach is the difficulty of establishing the control cohort. This difficulty disappears in family studies, which include their own controls. So far, the only results based on complex segregation analysis have been focused on parasite multiplication and not on cerebral malaria.

A role for cytokines in potentiation of malaria vaccines through immunological modulation of blood stage infection

Malaria is the world's major parasitic disease, for which effective control measures are urgently needed. One of the difficulties hindering successful vaccine design against Plasmodium is an incomplete knowledge of antigens eliciting protective immunity, the precise types of immune response for which to aim, and how these can be induced. A greater appreciation of the mechanisms of protective immunity, on the one hand, and of immunopathology, on the other, should provide critical clues to how manipulation of the immune system may best be achieved. We are studying the regulation of the balance between T helper 1 (Th1) and T helper 2 (Th2) CD4+ T lymphocytes in immunity to asexual blood stages of malaria responsible for the pathogenicity of the disease. Protective immunity to the experimental murine malarias Plasmodium chabaudi and Plasmodium yoelii involves both Th1 and Th2 cells, which provide protection by different mechanisms at different times of infection characterised by higher and lower parasite densities, respectively. This model therefore facilitates a clearer understanding of the Th1/Th2 equilibrium that appears central to immunoregulation of all host/pathogen relationships. It also permits a detailed dissection in vivo of the mechanisms of antimalarial immunity. Here, we discuss the present state of malaria vaccine development and our current research to understand the factors involved in the modulation of vaccine-potentiated immunity.