PLoS One. 2014 Feb 25;9(2):e89412.

Protein malnutrition impairs the immune response and influences the severity of infection in a hamster model of chronic visceral leishmaniasis.

Carrillo E1, Jimenez MA2, Sanchez C1, Cunha J3, Martins CM4, da Paixão Sevá A4, Moreno J1.
  • 1WHO Collaborating Centre for Leishmaniasis, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Madrid, Spain.
  • 2Departamento Medicina y Cirugía Animal, Facultad de Veterinaria, Universidad Complutense de Madrid, Madrid, Spain.
  • 3Instituto de Biología Molecular e Celular, Instituto de Ciências Biomédicas Abel Salazar e Faculdade de Medicina, Universidade do Porto, Porto, Portugal.
  • 4Departamento Medicina Veterinária Preventiva e Saúde Animal, Faculdade de Medicina Veterinária e Zootecnia da Universidade de São Paulo, São Paulo, Brazil.

 

ABSTRACT:

Leishmaniasis remains one of the world’s most devastating neglected tropical diseases. It mainly affects developing countries, where it often co-exists with chronic malnutrition, one of the main risk factors for developing the disease. Few studies have been published, however, on the relationship between leishmaniasis progression and malnutrition. The present paper reports the influence of protein malnutrition on the immune response and visceral disease development in adult hamsters infected with Leishmania infantum fed either standard or low protein diets. The low protein diet induced severe malnutrition in these animals, and upon infection with L. infantum 33% had severe visceral leishmaniasis compared to only 8% of animals fed the standard diet. The infected, malnourished animals showed notable leukocyte depletion, mild specific antibody responses, impairment of lymphoproliferation, presence of parasites in blood (16.67% of the hamsters) and significant increase of the splenic parasite burden. Animals fed standard diet suffered agranulocytosis and monocytopenia, but showed stronger specific immune responses and had lower parasite loads than their malnourished counterparts. The present results show that protein malnutrition promotes visceral leishmaniasis and provide clues regarding the mechanisms underlying the impairment of the immune system.

PMID: 24586759

 

SUPPLEMENT:

Leishmaniasis is a poverty-associated disease with several different forms, the most common being cutaneous leishmaniasis, usually presented as ulcers on exposed body parts, and visceral leishmaniasis which is fatal without treatment. Visceral leishmaniasis is a neglected disease that affects over 80 countries across Asia, East Africa, South America, and the Mediterranean region. Many people living in these countries suffer from malnutrition which is a major contributor to mortality and is increasingly recognized as a cause of, potentially lifelong, functional disability. Although the relationship between malnutrition and leishmaniasis is well established, few studies have measured the effects of malnutrition on the development of visceral leishmaniasis.

As one of the principal individual risk factors for disease development, malnutrition causes functional abnormalities in host defence systems affecting the resolution of Leishmania infection, because control of visceral leishmaniasis is mainly attributed to a strong acquired cell-immunity.

The primary cause of death in underdeveloped countries is protein-calorie malnutrition, therefor this study focuses on malnutrition caused by diet consumption. Animals were fed with commercial brands of a standard protein diet for rodents (14% content in protein) and a depleted protein diet (3% content in protein). We used the hamster model for the study of malnutrition-leishmaniasis interaction, because it is the rodent model that best reproduces the clinical spectrum of visceral leishmaniasis: anaemia, leukopenia, hepatosplenomegaly and bone marrow suppression. Although the effects of low and standard protein diets on certain parasitic infections have been previously studied in hamsters, this is the first study on leishmaniasis.

To study the influence of dietary protein malnutrition on the immune response and the outcome of Leishmania infantum infection, haematological, biochemical and immunological variables were analysed over 4 months in malnourished and well-nourished hamsters infected/non-infected with L. infantum. Differences in lymph node, bone marrow, spleen and liver parasite loads, and hepatic and splenic histopathology of infected animals were also studied.

Severe malnourishment produced alterations of most biochemical parameters and white cell subset counts in non-infected animals. In addition to leukopenia, malnourishment caused a diminished unspecific cellular response (concanavalin), which can hinder the ability of fighting infection. In fact, L.infantum infection in malnourished animals caused a worse manifestation of visceral disease in comparison to well-nourished animals. However, malnourished infected animals showed a similar biochemical and haematological pattern than non-infected, indicating the extreme conditions caused by severe malnutrition itself. Differences between groups were found mainly in their immunological responses and, consequently, in their parasite distribution. Most of well-nourished infected animals presented a patent specific response against SLA soluble leishmanial antigen, showing their capability to mount an efficient cellular immune response against Leishmania. On the contrary, malnourished infected animals showed an impaired response to leishmanial antigen and lower lymphocyte counts, particularly of CD4+ T cells. Further, malnourished infected animals induced the lowest lymphoproliferative response to unspecific stimuli comparing between all groups. These characteristics determined that malnourished animals have a lower capability of fighting against L.infantum infection and the development of a worse manifestation of visceral leishmaniasis in comparison to well-nourished animals. For that reason, malnourishment contributed to higher parasite loads, finding parasites even in non-visceral tissues, like blood.

The results showed that prolonged protein deprivation elicits a weakened immune response and promotes severe visceral leishmaniasis. Future experiments using this model of visceral leishmaniasis in malnutrition will be performed soon in order to study the intrinsic mechanisms involved in the cellular immune response and to evaluate if leishmanial vaccines may protect immunosuppressed hamsters. Knowing that leishmaniasis is a poverty-associated disease that co-exists with malnutrition, this animal model will contribute to elucidate the benefit of dietary supplementation before vaccination.

ACKNOWLEDGEMENTS

This work was funded by project PI10/00829 from the Fondo de Investigación Sanitaria.

 

Figure 1Fig 1. Cellular immune response. Lymphoproliferative response to specific against SLA soluble leishmanial antigen (A) and non-specific concanavalin CONA (B) stimuli, at 113 days post-infection, of peripheral blood mononuclear cell (PBMC) from infected and non-infected hamsters following the 14% and 3% protein diets.

 

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