Marcel Hommel

Evaluation of a urinary antigen‐based latex agglutination test in the diagnosis of kala‐azar in eastern Nepal

Background  We evaluated the diagnostic accuracy as well as the reproducibility of the urine latex agglutination test ‘KAtex’ in the diagnosis of kala‐azar in patients recruited at a tertiary care centre in Dharan, Nepal, between November 2000 and January 2002.

Plasmodium chabaudi: a rodent malaria model for in-vivo and in-vitro cytoadherence of malaria parasites in the absence of knobs.

Summary The ability of Plasmodium chabaudi infected erythrocytes to bind to endothelial cells in vivo and to various murine cell lines in vitro is described. A procedure for the selective recovery of a sequestering subpopulation of schizont‐infected erythrocytes from hepatic sinusoids of BALB/c mice, using a combination of body perfusion, trypsin treatment and Percoll density centrifugation was developed. The serial subinoculation of such a subpopulation was used to select for a clone of parasites (strain AJJ) with considerably better cytoadherent characteristics than the parent line (strain AJ). In contrast, it was demonstrated that another clone (PC7), showed no cytoadherence in vivo or in vitro. This study shows that parasite induced alterations occurred on the surface of erythrocytes infected with late developmental stages of P. chabaudi. The antigenicity of these molecules in the infected mouse was demonstrated using immune serum and affinity chromatography. Cytoadherence and surface antigenic changes in P. chabaudi schizont‐infected erythrocytes were demonstrated in the absence of the submembranous ‘knobs’ associated with cytoadherence in P. falciparum.

Antigenic variation in malaria parasites.

Antigenic variation and sequestration in organ capillary systems are two of the ways by which malaria parasites escape immune effector mechanisms. Here Marcel Hommel discusses the presence of variant antigens and endothelial-binding molecules on the surface of infected erythrocytes in the context of malaria immunity.

Markers of Loa loa infection in permanent residents of a loiasis endemic area of Gabon

Different markers of infection were analyzed in 56 permanent residents of a Loa loa endemic village in Gabon. The population was divided into those with parasitological evidence of L. loa infection and those with no history of loiasis over the period of observation (c. 5 years). 26.7% of villagers had L. loa microfilariae, 33.9% had an ocular passage of an adult worm, and 17.8% had calabar oedema. Several other clinical symptoms were present in both groups of individuals, but none was considered to be pathognomonic for L. loa infection. Most of the villagers were polyparasitized, with Plasmodium falciparum and gastrointestinal parasites being particularly prevalent. Mansonella perstans was present in 80% of the villagers and was equally distributed between L. loa microfilaraemic and amicrofilaraemic individuals. Eosinophil levels were elevated in the whole population, and were not significantly different between the groups who were infected and non-infected with L. loa. Polyclonal immunoglobulin (Ig) E levels were high in both the Ambinda villagers and in Gambian serum from patients infected with M. perstans alone and there was no significant difference between the levels of L. loa specific IgG in the Ambinda villagers and the Gambian patients. However, the level of L. loa specific IgG4 was elevated in 75.6% of amicrofilaraemic individuals and could discriminate between most individuals infected with L. loa and those infected with M. perstans, suggesting that this is the best determinant of infection status in the absence of L. loa microfilariae.

Cloning of a gene encoding the immunodominant surface antigen of Leishmania donovani promastigotes

This study describes the characterisation of externally oriented surface peptides of both morphological forms of Leishmania donovani, the causative agent of visceral leishmaniasis (kala-azar). Using 125I surface labelling techniques and peptide extraction in the detergents Triton X-100 and Triton X-114, a major iodinable promastigote peptide at 63 kDa or 65 kDa (depending on detergent used) was identified. This peptide was demonstrated to be the immunodominant membrane peptide of L. donovani and was strongly recognised by human sera from parasitologically confirmed cases of kala-azar. This peptide was not demonstrated on the surface of tissue amastigotes, although in vitro translations of poly(A+) RNA from both promastigotes and amastigotes demonstrated that both forms possessed mRNA that directs the synthesis of a 63 kDa peptide. It is suggested therefore that in amastigotes this peptide may be a processed antigen. We also report the isolation of a recombinant cDNA clone in the bacteriophage vector lambda gt10 which encodes a 63 kDa polypeptide that is recognised by human kala-azar sera. It is proposed that this surface peptide could be used in a specific immunodiagnostic test for leishmaniasis.

IgG subclass recognition of Loa loa antigens and their correlation with clinical status in individuals from Gabon

In endemic areas for Loa loa, a significant percentage of actively infected individuals have no circulating microfilariae, an observation which implies the existence of a stage‐specific immune response. In an attempt to define the immunological basis of the amicrofilaraemic state, the reactivity of antigens from adult, microfilariae and infective larvae of L. loa was examined by Western blotting with individual serum samples from four clinically defined groups (high microfilaraemic, low microfilaraemic, amicrofilaraemic and endemic controls) using IgG subclass‐specific reagents and IgE. In the adult parasite, a complex of antigens at 28‐31 kDa was exclusively recognized by IgG1 from amicrofilaraemic individuals and, to a lesser extent, by IgG1 from endemic controls. However, this complex of antigens was recognized by IgG4 antibodies in serum samples from all individuals, including microfilaraemics. A microfilarial antigen of 21 kDa was recognized by IgG1 antibodies present in serum from amicrofilaraemic, endemic control and low microfilaraemic individuals. Persons with high levels of microfilariae did not recognise this antigen. In both the L3 and the microfilariae, a ladder antigen with increments of 15 kDa was the main target of IgG4 antibodies in amicrofilaraemic and microfilaraemic individuals. IgE antibodies recognized more antigens in the microfilarial stage than in the adult of L3. These results suggest that immunological differences between clinically defined groups are associated with the recognition of different antigens or epitopes.

Amino-sugars inhibit the in vitro cytoadherence of Plasmodium falciparum-infected erythrocytes to melanoma cells

Twenty-two sugars and related compounds, nine neoglycoproteins, dopamine, four polyamines and oligomers of glucosamine were examined for their effect on the cytoadherence of Plasmodium falciparum-infected erythrocytes to melanoma cells. Inhibition of cytoadherence was high in the presence of the amino-sugars, glucosamine, galactosamine and mannosamine, and dopamine, and significant, although lower, in the presence of the polyamines, spermine, spermidine and putrescine. N-acetylated amino-sugars and the other compounds were not significant inhibitors of cytoadherence.

Modulation of host cell receptors : a mechanism for the survival of malaria parasites

Intra-erythrocytic stages of malaria parasites can alter the surface of their host cells and release toxins which induce the production of cytokines, which in turn can up- or down-regulate the expression of adhesion receptors on the surface of microvascular endothelial cells. New adhesion receptors on endothelial cells provide the parasite with increased chances of survival despite an increasing level of host immunity. In order to take advantage of these new opportunities for survival, the parasite itself needs to make best use of its considerable ability to vary its surface antigens and adherent molecules. The paper describes the various players in this survival game and articulates a working hypothesis to explain how it may all fit together.

Malaria, Microtubules and Merozoite Invasion

1571–1574 4 de Colmenares, M. et al. (1995) Am. J. Trop. Med. Hyg. 52, 427–428 5 Zheng, H. et al. (1987) Am. J. Trop. Med. Hyg. 31, 554–560 6 Freillij, H.L. and Corral, R.S. (1987) J. Clin. Microbiol. 25, 133–137 7 Katzin, A.M. et al. (1991) Am. J. Trop. Med. Hyg. 45, 453–462 8 Lieshout, L. Van et al. (1991) Am. J. Trop. Med. Hyg. 44, 323–328 Subash Chandra Parija is at the Department of Microbiology, B.P. Koirala Institute of Health Sciences, Dharan, Nepal. Tel: +977 25 20802, Fax: +977 25 20251, e-mail: bpkihs@npl.healthnet.org

The direct agglutination test : a non-specific test specific for the diagnosis of visceral leishmaniasis ?

Serology has an important role to play in the diagnosis of the severe clinical syndrome of visceral leishmaniasis (VL). The direct agglutination test (DAT), a simple agglutination test which requires no laboratory facilities, has become the preferred test, particularly for field studies. The nature of the antigens responsible for the agglutination of leishmanial promastigotes by the serum of VL patients is not known. A series of experiments which provide some clues to the molecular basis for the test and which indicate that there might be more in DAT than meets the eye is reported.