Michael Grigg, Ph.D.

Parasitic protozoa are serious pathogens of humans and animals throughout the world whose biology is quite remarkable. Studies investigating their cell and molecular biology have identified unique paradigms of eukaryotic pathogenesis, including antigenic variation, virulence shifts, RNA editing, and inactivation of host immune signaling networks to promote infection competency. The primary goal of the Molecular Parasitology Section is to understand the molecular basis of virulence and pathogenesis in the parasitic protozoa.

My research program investigates the evolution, phylogenetics, and immunopathogenesis of prevalent zoonoses, specializing in protozoan parasites including diplomonads (i.e., Giardia spp.), stremenopiles (i.e., Blastocystis spp.), amoebozoa (i.e.,Entamoeba spp.), parabasalids (i.e., Trichomonas spp.), kinetoplastids (i.e., Leishmania spp., Trypanosoma spp.), and the apicomplexa (i.e., Toxoplasma gondii, Neospora spp., Sarcocsytis spp., Cryptosporidia spp.). We perform whole genome sequencing, population genetic, and molecular epidemiology analyses to identify protozoal agents associated with epidemic disease, and we use both forward and reverse genetics to identify genetic determinants governing virulence shifts among the parasitic protozoa. Our primary focus is Toxoplasma, a serious pathogen capable of causing lethal infections in the developing fetus, immunocompromised patients, and blinding chorioretinitis in both children and adults. In all hosts, Toxoplasma establishes long-term chronic infections that persist for life despite the induction of strong immunity. Our work in Toxoplasma has identified parasite surface and secreted effector molecules that activate inflammasome pathways and dysregulate CD4 T-cell and B-cell activation. We also utilize pathogen-driven models of immune dysregulation to study the role of B-cell homing, regulatory T-cell function, and the gut microbiota in the regulation and maintenance of immune homeostasis in the context of inflammatory stimuli that contribute to or maintain the chronicity of intestinal inflammation. Eliminating the ability of the parasite to evade sterilizing immunity is central to controlling both its propagation and pathogenesis, as no vaccine or drug is currently capable of doing this. Our research is contributing valuable insight into parasite-specific molecular strategies of eukaryotic pathogenesis. The expansion of our research focus to study Leishmania, Entamoeba, Trichomonas, and Giardia is largely the result of our continuing effort to identify how other Category B pathogens have evolved to subvert host innate and adaptive immune responses to facilitate their survival, transmission, and success.

Current work in the Molecular Parasitology Section is divided into the following four projects: 1) To assess the contribution of sexual reproduction in the evolution of new, virulent strains of protozoan pathogens, we are investigating outbreaks associated with unusually severe clinical disease by sequencing Giardia, Leishmania, Toxoplasma, Sarcocystis, Neospora, andCryptosporidia isolates in order to identify genetic determinants governing “virulence shifts” in the parasitic protozoa; 2) To identify parasite genes essential for entry into host cells, colonization, and subversion of host immunity, we have developed a combination of functional genomic and genetic screens and molecular imaging techniques to determine the molecular interactions controlling protozoan parasite pathogenesis in naturally infectious murine disease models; 3) To investigate how parasite surface antigens regulate host immunity and contribute to parasite infectivity, we are analyzing gene expression and performing structural, immunological, and gene knock-out analyses to disrupt parasite colonization and persistence; and 4) To discover proteins essential for completion of the Toxoplasma sexual cycle, we are generating sexual life cycle stage-specific transcriptome data (e.g.,merozoite, gametocyte, zygote) and using transgenic and reverse genetic strategies to identify bona fidetargets for transmission blocking interventions and vaccine development.

Our major projects include the following:

• Investigating protozoan outbreaks associated with unusually severe clinical disease to assess the contribution of sexual meioses in the evolution of new strains that possess altered biological potential
• Pursuing functional genomic, genetic, and bioinformatic approaches to identify and characterize discrete virulence factors that contribute to protozoan disease pathogenesis
• Bioimaging the host-pathogen interaction in vivo using real-time molecular imaging and in situ within anatomically intact host tissues to visualize host immune cells responding to parasite-infected targets
• Determining changes in gene expression and pursuing structural and immunological analyses to investigate how parasite cell-surface antigens that regulate host immunity contribute to parasite infectivity

Because relatively little is known about eukaryotic pathogenic processes as compared to the field of bacterial or viral pathogenesis, it is likely that entirely new mechanisms and principles of pathogenesis will emerge from our work.