Immune-dependence of chemotherapy of experimental visceral leishmaniasis

Efficacy of human beta-casein fragment (54-59) and its synthetic analogue compound 89/215 against Leishmania donovani in hamsters

The characteristic feature of visceral leishmaniasis (VL) is the profound impairment of immune system of the infected host, which contributes significantly to the partial success of antileishmanial chemotherapy. Since in VL, cure is the combinatorial effect of drug and immune status of the host, the rationale approach towards antileishmanial chemotherapy would be to potentiate the immune functioning of the host to extract desired results. Towards this direction several rationally designed analogues of human beta-casein fragment (54-59) were evaluated for their ability to stimulate the non-specific resistance in hamsters against Leishmania donovani infection. By virtue of being derived from the food protein casein derivatives may be devoid of unwanted side effects associated with the substances of microbial origin, e.g. muramyl dipeptide (MDP). Out of this one peptide Val-Glu-Gly-Ile-Pro-Tyr (compound 89/215) had been reported to have such activity. In this communication, the prophylactic and therapeutic efficacy of the peptide along with its natural sequence has been evaluated in detail against experimental VL in hamsters. Their use as an adjunct to chemotherapy was also explored. Human beta-casein fragment, compound 89/215 and MDP were tested in vivo at various dose levels wherein compound 89/215 showed superiority over MDP at 3 mg/kg x 2 given intraperitoneally (i.p.). Compound 89/215 sensitized peritoneal macrophages acquired considerable resistance and only 24% of the cells were found infected in comparison to control peritoneal macrophages where 76.4% of the cells were found infected. Similarly, the efficacy of sodium antimony gluconate (SAG) in hamsters pretreated with compound 89/215 enhanced significantly (P < 0.001). This peptide also exhibited considerably good therapeutic efficacy when evaluated either alone or in combination with SAG in established infection of L. donovani.

Evaluation of immune dependence of anthelmintic treatment of Heligmosomoides polygyrus in CBA/Ca mice

The efficacy of anthelmintic treatment of adult Heligmosomoides polygyrus was evaluated in immunologically intact and immune-incompetent (T-cell-deprived) CBA/Ca mice. There was no statistically significant difference in the cure rate, in terms of percentage reduction in worm burden, following treatment with pyrantel pamoate and levamisole between normal (57-71% reduction) and immune-incompetent mice (69-78% reduction). The rate of expulsion, and the total number, of worms expelled from infected mice following drug treatment were comparable in normal and deprived mice. The activity of 2 drugs against adult H. polygyrus has been shown to be independent of the immune status of the host. The significance of the mode of actions of drugs and the site of residence of a parasite within the host are discussed.

Genetic control of drug-induced recovery from murine visceral leishmaniasis

The influence of host genetic background on the response of Leishmania donovani-infected mice to chemotherapy was studied using the H-2d and H-2b haplotypes on a BALB or a B10 genetic background. Animals were treated with free or liposomal sodium stibogluconate and parasite burdens in the liver, spleen and bone marrow were assessed. In all the mouse strains and their congenic derivatives examined, the liver responded best to therapy regardless of drug formulation, whilst the spleen and the bone marrow respectively were increasingly less responsive to chemotherapy. Treatment with free drug was more effective in congenic mice carrying the H-2b haplotype than in those carrying the H-2d haplotype and in mice carrying the same H-2 haplotype, animals from a BALB background were better responders than those from a B10 genetic background. Liposomal drug was more effective than free drug treatment in all four mouse strains and produced a similar significant suppression (> 99%, P < 0.001) in liver parasite burdens to that obtained using a six times greater free drug dose. This liposomal drug dose was more effective than free drug in reducing bone marrow parasite burdens in all four mouse strains and equally (BALB/c mice) or more effective (P < 0.01, BALB/B, B10 and B10.D2 strains) in reducing spleen parasite numbers. Liposomal dependent influences apparent using free sodium stibogluconate. These results are discussed in relation to the genetic factors which are known to control the course of L. donovani infection in mice.

The rapid development of drug-resistance by Trypanosoma evansi in immunosuppressed mice

The effect of immunosuppression on the development of drug resistance by trypanosomes was investigated in mice infected with Trypanosoma evansi. As a result of frequent passage in immunosuppressed mice given subcurative drug treatments clones of T. evansi rapidly developed high levels of resistance to mel Cy, diminazene aceturate and isometamidium chloride. Similar protocols in normal immunocompetent mice infected with the same parent clones did not lead to the development of drug-resistance. The resistant populations developed in immunosuppressed mice maintained their high levels of resistance when tested in normal mice. The mel Cy resistant clone was tested for cross-resistance to other trypanocides and was found to be also highly resistant to diminazene and pentamidine. The results indicate that impairment of the host immune system may lead to the rapid development of drug-resistance by T. evansi under experimental conditions in mice and may possibly play a role in the development of drug resistance by trypanosomes in the field.

Chemotherapy and immunity in opportunistic parasitic infections in AIDS

Parasitic diseases are endemic in parts of the tropics, but there is no convincing evidence that their prevalence or incidence is increasing due to the HIV epidemic. Available scientific data on parasitic infections in patients with the Acquired Immunodeficiency Syndrome (AIDS) suggests a predominance of Pneumocystis carinii, Toxoplasma gondii and Cryptosporidium spp. For reasons which are unclear, parasitic infections such as Plasmodium falciparum, Strongyloides stercoralis and Entamoeba histolytica, where cell-mediated immune responses are also thought to be significant, do not appear to be opportunists of importance. It is being increasingly recognized that chemotherapy for parasitic diseases has a host-dependent component, although scientific data on this subject remain scanty. The management of opportunistic parasitic infections in patients infected with HIV is dogged by failures and relapses, aptly illustrating the notion of the relationship between chemotherapy and the immune response. This review discusses the immunity and chemotherapy of opportunistic parasite infections in patients infected with the Human Immunodeficiency Virus (HIV).

Interactions between immunity and chemotherapy in the treatment of the trypanosomiases and leishmaniases

The immune status of a host infected with Trypanosoma spp. or Leishmania spp. can play an important role in successful chemotherapy. In animal models, treatment of African trypanosomiasis with difluoromethylornithine or melarsoprol requires an appropriate antibody-mediated immune response. An intact immune system is also necessary for rapid clearance of trypanosomes from the bloodstream following treatment with suramin or quinapyramine. Similarly, an efficient cell-mediated immune responses is required for maximal efficacy of pentavalent antimonials in the treatment of leishmaniasis. However, the potential relationship between parasite-induced or acquired immunosuppression and effective chemotherapy has been poorly studied. Macrophages which have been activated by bacterial cell wall components or gamma-interferon are known to display increased activity against Leishmania donovani or Trypanosoma cruzi. In experimental and clinical visceral leishmaniasis, use of macrophage activators together with pentavalent antimonials has lowered the dose of antimony required to cure the infection.