Molecular determinants and regulation of Leishmania virulence

A Leishmania model to explain microbial virulence in chronic infectious diseases is proposed. All these diseases progress from infection to symptomatic phase to host death or recovery. The outcome of each phase is depicted to result from the interactions of a distinct group of parasite molecules with a specific host immune compartment. The first group consists of invasive/evasive determinants, which are largely parasite cell surface and secreted molecules. Their activities help parasites establish infection by overcoming host immunologic and non-immunologic barriers. These determinants do not cause disease per se, but are indispensable for infection necessary for the development of a disease-state. The second group of parasite molecules consists of "pathoantigenic" determinants – unique parasite epitopes present often within otherwise highly conserved cytoplasmic molecules. Immune response against these determinants is thought to result in immunopathology manifested as clinical signs or symptoms, namely the virulent phenotype. The third group of parasite molecules is hypothetically perceived as vaccine determinants. Their interactions with the host immune system lead to the elimination or reduction of parasites to effect a clinical cure. Differential expression of these determinants alone by parasites may alter their interactions with the hosts. Virulent phenotype is consequently presented as a spectrum of manifestations from asymptomatic infection to fatality. A secondary level of regulation lies in host genetic and environmental factors. The model suggests that different parasite determinants may be targeted by different strategies to achieve more effective control of leishmaniasis and other similar diseases

Host-Directed Drug Therapies for Neglected Tropical Diseases Caused by Protozoan Parasites

The neglected tropical diseases (NTDs) caused by protozoan parasites are responsible for significant morbidity and mortality worldwide. Current treatments using anti-parasitic drugs are toxic and prolonged with poor patient compliance. In addition, emergence of drug-resistant parasites is increasing worldwide. Hence, there is a need for safer and better therapeutics for these infections. Host-directed therapy using drugs that target host pathways required for pathogen survival or its clearance is a promising approach for treating infections. This review will give a summary of the current status and advances of host-targeted therapies for treating NTDs caused by protozoa

Migration through the Extracellular Matrix by the Parasitic Protozoan Leishmania Is Enhanced by Surface Metalloprotease gp63

Leishmania species engineered to express high levels of the surface metalloprotease gp63 have enhanced capacity of migration through extracellular matrix in vitro. This correlates with gp63 degradation of extracellular matrix components, such as collagen type IV and fibronectin, and suggests an important role for gp63 in the pathogenesis of leishmaniasis

Fibronectin Binding and Proteolytic Degradation by Leishmania and Effects on Macrophage Activation▿

Infection by vector-borne protozoa of the genus Leishmania occurs by the deposition of parasites within the skin of the mammalian host, where they eventually bind to and are phagocytized by Mφs. Our previous work supported the idea that parasites can interact with extracellular matrix and basement membrane proteins, such as fibronectin (FN), within the skin, leading to enhanced invasion. In this report, we extend these findings and show that both promastigotes and amastigotes of Leishmania species can bind directly to soluble FN and laminin (LM) and that promastigotes express a distinct surface protein of ∼60 kDa that binds both FN and LM. Promastigotes of multiple Leishmania species can rapidly degrade FN by using surface-localized and secreted metalloprotease (leishmanolysin). FN degradation at the surfaces of amastigotes is leishmanolysin dependent, whereas both secreted leishmanolysin and cysteine protease B contribute to extracellular FN degradation. Leishmania-degraded FN decreased the production of reactive oxygen intermediates by parasite-infected macrophages and affected the accumulation of intracellular parasites. These findings show that both parasite stages of Leishmania species bind to and proteolytically degrade FN at the parasite surface and distantly through secreted proteases and that degraded forms of FN can influence the activation state of parasite-infected macrophages

Trypanosoma cruzi GP63 Proteins Undergo Stage-Specific Differential Posttranslational Modification and Are Important for Host Cell Infection ▿

The protozoan Trypanosoma cruzi expresses multiple isoforms of the GP63 family of metalloproteases. Polyclonal antiserum against recombinant GP63 of T. cruzi (TcGP63) was used to study TcGP63 expression and localization in this organism. Western blot analysis revealed that TcGP63 is 61 kDa in epimastigotes, amastigotes, and tissue culture-derived trypomastigotes but 55 kDa in metacyclic trypomastigotes. Antiserum specific for Leishmania amazonensis GP63 specifically reacted with a 55-kDa TcGP63 form in metacyclic trypomastigotes, suggesting stage-specific expression of different isoforms. Surface biotinylation and endoglycosidase digestion experiments showed that TcGP63 is an ecto-glycoprotein in epimastigotes but is intracellular and lacking in N-linked glycans in metacyclic trypomastigotes. Immunofluorescence microscopy showed that TcGP63 is localized on the surfaces of epimastigotes but distributed intracellularly in metacyclic trypomastigotes. TcGP63 is soluble in cold Triton X-100, in contrast to Leishmania GP63, which is detergent resistant in this medium, suggesting that GP63 is not raft associated in T. cruzi. Western blot comparison of our antiserum to a previously described anti-peptide TcGP63 antiserum indicates that each antiserum recognizes distinct TcGP63 proteins. Preincubation of trypomastigotes with either TcGP63 antiserum or a purified TcGP63 C-terminal subfragment reduced infection of host myoblasts. These results show that TcGP63 is expressed at all life stages and that individual isoforms play a role in host cell infection