Identification of amastigote-specific antigens of Leishmania donovani using kala-azar patient sera.

Antigenic characterization of the soluble fraction of axenic amastigotes of Leishmania donovani ( strain Dd8, causative agent of Indian kala-azar) and their comparison with promastigotes is reported. The axenic amastigotes were assessed for their immunological status employing anti-A2 monoclonal antibody which is extremely specific for L. donovani amastigotes. SDS-PAGE of 35[S] methionine labeled proteins of the two parasite stages exhibited few stage specific and some conserved antigens in both the stages. An increased synthesis of heat shock proteins was observed in axenic amastigotes. Western blot experiments employing sera of kala azar positive patients identified immunodominent antigens of 116,83,26 and 12 kDa in axenic amastigotes which were not present in promastigotes. These amastigote stage specific antigens may have immense potential in immunodiagnosis and prophylaxis of kala-azar.

Immune response against the non-repeat region (293-310) of the circumsporozoite protein of Plasmodium vivax.

Immunization by peptides based on the repeat sequences of Plasmodium falciparum or P. vivax antigen(s) have shown inconsistent results during clinical trials in humans. This could be attributed to the lack of T-cell help or antigenic polymorphism. Thus, attention has been focused towards the more conserved non-repeat regions. The present study was undertaken to map the antigenic determinant in the vicinity of region II (outside the repeat) of CS protein of P. vivax. The immunogenicity of the peptide was studied alone and after linking with polytuftsin (PT), using alum and Freund's adjuvant, in inbred strains of mice with different genetic backgrounds. The humoral response and antigen induced T-cell proliferation assays clearly demonstrated the immunomodulatory activity of PT. Comparable results were observed with antigen(s) administered either in alum or Freund's adjuvant. The induction of IgG2a and IgG2b antibody isotypes by both, peptide as well as the conjugate, may indicate that the T-helper response involved is of Th1 type. Further the immunofluorescence studies have shown that antibodies recognized the air dried sporozoites of P. cynomolgi. The results thus show that the above sequence has overlapping B and T-cell determinants and that alum can be substituted for Freund's adjuvant in generating an effective immune response.

Current trends in research on tissue stage of malaria.

The tissue stage or the exoerythrocytic (EE) stage of the malaria parasite, for many years remained the most neglected form mainly because of its inaccessibility being located in the liver. The advent of in vitro techniques resulting in the successful cultivation of these forms in primary hepatocyte cultures and a variety of cell lines has greatly augmented research on these stages and have provided unique in vitro systems which can be used as primary screens for candidate chemotherapeutic and immunoprophylactic agents and have facilitated better understanding of the sporozoite-hepatocyte interactions. Sensitive and specific nucleic acid probes (DNA and ribosomal RNA) have been developed to quantify EE stages in infected livers. Efforts to establish SCID mouse as a model for cultivation of EE stages of human malaria parasites have been encouraging. The earlier assumptions that these tissue stages are free from immune attack have been proven wrong and the hepatic phase itself now appears to be essential for the induction of protection against the pre-erythrocytic stages. Liver stage specific antigens have been identified in recent years. Despite its intracellular position, this 'hidden' form has been found to constitute a target for antibodies, cytokines, and cytotoxic T cells. The present review focuses on the advances in research on the 'silent' stage of malaria parasites.

Studies on heme and heme oxygenase during Plasmodium berghei infection in golden hamsters.

Heme and heme degrading enzymes namely heme-oxygenase (HO) and biliverdin reductase (BR) were monitored in liver and spleen during Plasmodium berghei infection in golden hamsters. There was a sequential rise in the levels of heme and HO with the rise in parasitaemia. BR was also significantly increased in these organs following infection.