Host Parasite Interactions of Cryptosporidium
Our research is focused on the apicomplexan parasite Cryptosporidium which causes diarrheal disease in humans worldwide. Cryptosporidiosis is asymptomatic or self-limiting in immunocompetent hosts but may be severe, chronic and life threatening in immunocompromised patients, such as those with acquired immunodeficiency syndrome (AIDS). Cryptosporidium has caused several outbreaks of waterborne disease worldwide. Because of the potential for intentional contamination of water supplies, Cryptosporidium is listed as a Category B Priority Pathogen for Biodefense by the Centers for Disease Control.
There are 2 major Cryptosporidium species that cause human infections; C. hominis primarily infects humans whereas C. parvum infects humans as well as other animals. Nitazoxanide is the only drug approved in the USA by the Food and Drug Administration for use in immunocompetent individuals with cryptosporidiosis. However, this drug is not effective against cryptosporidial infection in immunocompromised hosts. There is currently no vaccine available for cryptosporidiosis. Therefore the continued search for novel preventive and therapeutic strategies is critical.
The pathogenic mechanisms by which C. parvum causes disease are unknown. In addition, little is known about specific parasite and host molecules involved in host-parasite interactions or about protective immune responses. Our overall goal in the study of cryptosporidiosis is to further our understanding of the molecular basis of Cryptosporidium-host cell interactions and to investigate immune responses to this parasite. Understanding the molecular mechanisms underlying the host-parasite interaction may lead to the development of specific interventions targeted at inhibiting this interaction. Identifying the mechanisms underlying protective immunity could lead to the development of immune-based preventive and therapeutic anti-cryptosporidial strategies.
Molecular basis of Cryptosporidium spp. attachment to and invasion of host cells
We have cloned and characterized a Cryptosporidium gene, Cpgp40/15 that encodes a major surface glycoprotein, gp40/15. This glycoprotein is proteolytically processed into two glycopeptides, gp40 and gp15 which associate with each other on the surface of the parasite and mediate attachment and invasion. The Cpgp40/15 locus is highly polymorphic in human isolates, a finding consistent with its gene products being surface-associated virulence determinants which may be under selective host immune pressure. Current efforts in our laboratory are directed at 1) Characterization of the glycotopes on gp40; 2) Investigation of immune responses to glycosylated and non-glycosylated, conserved and polymorphic domains of gp40 3) Investigation of proteases involved in post-translational processing of gp40/15; 4)Investigation of polypeptide-N-acetylgalactosaminyl transferases which catalyze the synthesis of glycotopes on gp40. The long term goal is to determine whether gp40/15 and its products, or enzymes which post-translationally modify them may serve as targets of drug or vaccine development.
Figure 1. p 30 in merozoites. Green, gp15 surface protein; Red, p30.
We have also cloned and characterized a galactose and N-acetyl-galactosamine(Gal/GalNAc)-specific sporozoite lectin named p30 which binds to Gal/GalNAc–mucins on the host as well as the parasite and mediate attachment. We also showed that Cryptosporidium sporozoites themselves express Gal/GalNAc-containing mucin-like surface glycoproteins such as gp40 and gp900 which associate with p30 and also mediate adhesion. Current studies are directed at investigating the role of parasite and host lectins and glycans in host-parasite interactions. The long term goal is to determine whether these molecules may serve as targets for prophylactic or therapeutic interventions.
International studies of Infectious Intestinal Diseases
In collaboration with investigators in resource constrained countries we are conducting cross sectional and longitudinal studies of infectious diarrheal diseases, particularly cryptosporidiosis in children and in HIV-infected adults. We are investigating systemic and mucosal Cryptosporidium-specific humoral and cell-mediated immune responses to specific antigens which are putative vaccine candidates in these individuals. We are also performing multi-locus genotypic analysis of Cryptosporidium spp. isolated from them and correlating genetic information with clinical, geospatial, epidemiological and immunological parameters.
New areas of research are directed at investigating the role of the intestinal microbiota and the use of probiotics for infectious diarrhea in children and in HIV-infected adults. The long term goal of these studies is the logical development of interventions such as vaccines and therapeutics that are appropriate to the communities in which the burden of these diseases is greatest.