The Trypanosoma cruzi Protease Cruzain Mediates Immune Evasion

Abstract

Trypanosoma cruzi is the causative agent of Chagas' disease. Novel chemotherapy with the drug K11777 targets the major cysteine protease cruzain and disrupts amastigote intracellular development. Nevertheless, the biological role of the protease in infection and pathogenesis remains unclear as cruzain gene knockout failed due to genetic redundancy. A role for the T. cruzi cysteine protease cruzain in immune evasion was elucidated in a comparative study of parental wild type- and cruzain-deficient parasites. Wild type T. cruzi did not activate host macrophages during early infection (<60 min) and no increase in ∼P iκB was detected. The signaling factor NF-κB P65 colocalized with cruzain on the cell surface of intracellular wild type parasites, and was proteolytically cleaved. No significant IL-12 expression occurred in macrophages infected with wild type T. cruzi and treated with LPS and BFA, confirming impairment of macrophage activation pathways. In contrast, cruzain-deficient parasites induced macrophage activation, detectable iκB phosphorylation, and nuclear NF-κB P65 localization. These parasites were unable to develop intracellularly and survive within macrophages. IL 12 expression levels in macrophages infected with cruzain-deficient T. cruzi were comparable to LPS activated controls. Thus cruzain hinders macrophage activation during the early (<60 min) stages of infection, by interruption of the NF-κB P65 mediated signaling pathway. These early events allow T. cruzi survival and replication, and may lead to the spread of infection in acute Chagas' disease.

Author Summary

Trypanosoma cruzi ( T. cruzi) is the unicellular parasite that causes Chagas' disease, a devastating health burden throughout Latin America now also affecting developed countries. Macrophages are the first cells that become infected by T. cruzi and disseminate the infection to other tissues. The parasite then preferentially infects and multiplies within heart muscle cells causing severe heart disease and often death. The new drug K11777 targets a vital parasite enzyme, the protease cruzain. Consequently, it is important to understand what the enzyme is doing during infection. To elucidate the role of the protease, we compared infection of macrophages with parental wild type parasites and with protease deficient T. cruzi. We now report a role for the parasitic protease in immune evasion. The protease prevents macrophage activation thus allowing T. cruzi survival and replication, and favoring the spread of infection.