Background: Protein energy malnutrition is commonly associated with immune dysfunctions and is a major factor
in susceptibility to infectious diseases.
Methods: In this study, we evaluated the impact of protein energy malnutrition on the capacity of monocytes and
macrophages to upregulate arginase, an enzyme associated with immunosuppression and increased pathogen
replication.
Results: Our results show that monocytes and macrophages are significantly increased in the bone marrow and
blood of mice fed on a protein low diet. No alteration in the capacity of bone marrow derived macrophages
isolated from malnourished mice to phagocytose particles, to produce the microbicidal molecule nitric oxide and
to kill intracellular Leishmania parasites was detected. However, macrophages and monocytes from malnourished mice
express significantly more arginase both in vitro and in vivo. Using an experimental model of visceral leishmaniasis, we
show that following protein energy malnutrition, the increased parasite burden measured in the spleen of these mice
coincided with increased arginase activity and that macrophages provide a more permissive environment for parasite
growth.
Conclusions: Taken together, these results identify a novel mechanism in protein energy malnutrition that might
contributes to increased susceptibility to infectious diseases by upregulating arginase activity in myeloid cells.