Research:

Many parasites target antigens as well as mechanisms involving acquired immunity in host resistance to protozoan infections have been defined over the years. However, the same cannot be said about innate immune mechanisms involved in initial host resistance, initiation of immune responses and pathogenesis during infection with this class of pathogens. The lack of information in this area seems to be an important impediment for development of effective prophylactic as well as therapeutic immunologic-based protocols to prevent or treat these diseases.  Therefore, the main scientific interests of my laboratory are: (i) to understand the role of innate immunity on host resistance and pathogenesis to infection with protozoan parasites; and (ii) to develop vaccines that induce cell-mediated immunity and protection against protozoan infections. When possible, we try to address our questions regarding host-parasite interactions, employing cellular systems, experimental rodent models and primary cells derived from well-characterized patients undergoing specific protozoan infection. My research program is developed at the Division of Infectious Diseases and Immunology, Department of Medicine, UMASS Medical School and at Oswaldo Cruz Foundation / Federal University of Minas Gerais, in Brazil.

Innate Immunity

IFNg seems to be a primary cytokine involved in host resistance and infection with protozoan parasites. The early studies describing the counter-regulatory role of IL-10 and IL-12 were important to understand the induction of IFNg by Natural Killer cells as well as on differentiation of CD4+ T lymphocytes towards the Th1 phenotype during infection with protozoan parasites. These studies were also essential to understand induction/evasion of cell mediated immunity, and thus explain a major mechanism of susceptibility/resistance as well as pathogenesis of infection with distinct parasitic protozoa. Currently, we are very interested in identifying cognate innate immune receptors for protozoan parasites and how they participate in the induction phase of cell mediated immunity and development of protective acquired immunity against this class of pathogens. We hope that these studies will contribute with a more rational design of effective vaccines against protozoan parasites, and new strategies to interfere with hypo-responsiveness (may favor parasite growth) or hyper-responsiveness (may be deleterious to the host), immunological status that are often associated with pathogenesis and lethality observed during protozoan infections. Below I provide a short summary of the research performed in my laboratory, which employ different protozoan parasites.

Chagas Disease - We have characterized the structure and function protozoan-derived glycosylphosphatidylinositol anchors (GPIs) as well as genomic unmethylated CpG motifs derived from T. cruzi parasites, which possess potent pro-inflammatory activities. We have also defined Toll-Like Receptors 2 and 9 as the host counterpart receptors for GPIs and CpG motifs both in mouse and human systems. In addition, we demonstrated the role of MyD88, TLR2 and TLR9 in early pro-inflammatory response and host resistance to infection with T. cruzi in mice and potential implications on immunopathology of Chagas' disease in humans are being considered. Questions regarding the involvement of TLRs and other innate immune receptors on pathogenesis of Chagas disease, the mechanisms of induction of cell mediated immunity as well as the use of T. cruzi derived agonists as vaccine adjuvants are currently being approached in my lab.

Malaria - We have also investigated the role of different TLRs and MyD88 in host resistance to infection and malaria pathogenesis. Together, our findings suggest that MyD88 and possibly its associated TLRs expressed by dendritic cells play an important role in pro-inflammatory responses, T cell activation, and pathogenesis of malaria, but are not critical for the immunological control of the erythrocytic stage of P. chabaudi. By in silico analysis and in vitro assays, we have defined CpG as well as AT rich motifs that activate human TLR9 and a new category of cytoplasmatic receptors. We have also shown that TLR responses are boosted in febrile patients during natural infection with P. falciparum. Microarray analyses demonstrated that an extraordinary percentage of the up-regulated genes, including genes of TLR signaling pathway, had sites for IFN-inducible transcription factors. Consistently, acutely infected wild-type mice were highly susceptible to LPS-induced lethality while TLR9-/-, and to a greater extent, IFNg -/- mice were protected. Our data provide unprecedented evidence that TLR9 and MyD88 are essential to initiate IFNγ responses and favor host hyper-responsiveness to TLR agonists resulting in overproduction of pro-inflammatory cytokines and the sepsis-like symptoms of acute malaria. We are currently trying to map the array of innate immune receptors and signaling pathways involved on early pro-inflammatory responses and sepsis symptoms/signs observed during P. falciparum malaria.

Toxoplasmosis  – MyD88 has also been shown critical in eliciting IL-12/IFNg production and host resistance to infection with T. gondii. However, none of the single TLR deficient mice seem to recapitulate the susceptibility of MyD88-/- mice to infection with this parasite. Our main goal is to establish what receptor(s) are responsible for MyD88 dependent activity during T. gondii infection. In parallel we are studying the innate immune responses to patients with asymptomatic and ocular toxoplasmosis. We have currently shown that human TLR2 / TLR4 and TLR9 are responsive to T. gondii derived GPI anchors as well as unmethylated CpG motifs, respectively. Further, the presence of specific gene variants (polymorphisms) associated with outcome of acquired immune responses and ocular disease are under evaluation. 

Vaccine Development

In regard to vaccine development two main issues have been investigated in my lab: (i) the question of appropriate antigen delivery and (ii) the use of specific TLR agonists as vaccine adjuvants to induce a strong cell-mediated immunity, including CD8+ T cell responses.  For the first question, we have engineered protective antigens from T. cruzi (ASP and TS); T. gondii (SAG1, SAG2 and SAG3); and Leishmania sp. (A2) into different viral vectors, i.e. adenovirus, MVA and influenza. In addition, these same antigens are being tested in association with well defined TLR agonists. The different protocols are being tested in the rodent model, as well as in primates and dogs in the case of leishmaniasis. The involvement of different components of innate as well as acquired immunity are being defined in various knockout mice that receive vaccination protocols that are effective protecting wild type controls against experimental challenges. Finally, GPI anchors and CpG motifs derived from T. cruzi  are being tested as potential novel immunological adjuvants in vaccine formulations.

Financial Support:  My current research is supported by Conselho Nacional de Desenvolvimento Cinetifico e Tecnologico-CNPq, Fundacao de Amparo a Pesquisa do Estado de Minas Gerais-FAPEMIG, the National Institutes of Health-NIH and the Atlantic Philanthropies / Ludwig Institute for Cancer Research.