Toxoplasma gondii is an opportunistic parasite that infects one-third of the global population and is among the most frequent causes of central nervous system (CNS) infection complicating AIDS. T. gondii establishes a chronic infection in the CNS, and immune compromise due to HIV infection leads to parasite reactivation and fatal encephalitis. This proposal addresses a poorly understood aspect of parasite pathogenesis during clinical AIDS - how does T. gondii migrate through the brain? Evidence suggests that T. gondii infection of migratory leukocytes facilitates the colonization of vital organs such as the brain via a 'Trojan horse' mechanism. Monocytes in particular are highly motile cells and a target for T. gondii infection. Our strong preliminary data demonstrate that T. gondii infection of human monocytes induces a hypermigratory phenotype and dysregulates the function of key adhesion molecules called integrins. The objective of this proposal is to define how T. gondii induces monocyte motility and disseminates through the brain. The central hypothesis is that T. gondii spreads through tissues by co-opting the migratory potential of infected cells.
Two aims are proposed to test the hypothesis: 1) Determine how T. gondii enhances the migration of infected cells, and 2) Define how T. gondii disseminates through the infected brain. In the first aim, we will investigate the regulation of integrin signaling and focal adhesion formation in infected primary human monocytes from healthy donors and from HIV patients. We will determine the role of focal adhesion kinase (FAK) by using monocytes expressing mutant variants of FAK that are constitutively active or non-phosphorylatable (inactive). We will also determine the interactions of the scaffolding molecules talin and paxillin with FAK and the dynamics of their assembly and disassembly in infected monocytes during migration. In the second aim, we will use intravital two-photon imaging and an animal model for T. gondii infection to define the myeloid cell type(s) that are infected and potentiate parasite spread through the mouse brain. Transgenic mice that express fluorescently labeled monocytes or microglia will be infected with T. gondii. The dynamics of their migration through the parenchyma will be determined during acute infection and in chronically infected mice undergoing parasite reactivation due to immune suppression. All of the necessary reagents are on hand in the lab or commercially available, and all the techniques, including biochemical and migration assays, total internal reflection fluorescence (TIRF) microscopy, and intravital imaging, are currently employed by our research team. The significance of this research is that understanding T. gondii dissemination may allow for therapeutic targeting of this process to mitigate disease during AIDS. The proposal is innovative because it applies a multidisciplinary approach and novel tools to identify the cellular and molecular mechanisms that mediate T. gondii dissemination in vitro and in vivo, which will ultimately shed light on a key aspect of parasite pathogenesis in HIV/AIDS patients.

Public Health Relevance

Toxoplasma gondii is an opportunistic parasite that can cause life-threatening encephalitis in HIV/AIDS patients. The proposed research is relevant to public health because it is expected to determine the cellular and molecular mechanisms used by the parasite to infect and spread through the brain of infected hosts. An understanding of this process may allow for targeted interventions that limit parasite dissemination and disease.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Research Project (R01)
Project #
Application #
Study Section
AIDS-associated Opportunistic Infections and Cancer Study Section (AOIC)
Program Officer
Wali, Tonu M
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
University of California Irvine
Schools of Arts and Sciences
United States
Zip Code
Lima, Tatiane S; Gov, Lanny; Lodoen, Melissa B (2018) Evasion of Human Neutrophil-Mediated Host Defense during Toxoplasma gondii Infection. MBio 9:
Cook, Joshua H; Ueno, Norikiyo; Lodoen, Melissa B (2018) Toxoplasma gondii disrupts ?1 integrin signaling and focal adhesion formation during monocyte hypermotility. J Biol Chem 293:3374-3385
Gov, Lanny; Schneider, Christine A; Lima, Tatiane S et al. (2017) NLRP3 and Potassium Efflux Drive Rapid IL-1? Release from Primary Human Monocytes during Toxoplasma gondii Infection. J Immunol 199:2855-2864
Chen, E Y; Chu, S; Gov, L et al. (2017) CD200 modulates macrophage cytokine secretion and phagocytosis in response to poly(lactic co-glycolic acid) microparticles and films. J Mater Chem B 5:1574-1584