Host - Parasite Interactions of Cryptosporidium

Our research focuses on host-parasite interactions of the intestinal protozoan parasites Cryptosporidium spp. Studies in our laboratory are directed at three aspects of these interactions.

Molecular basis of Cryptosporidium spp. attachment and
invasion of host intestinal epithelial cells

These studies are focused on investigating specific parasite and host molecules, which mediate attachment and invasion and which may serve as potential targets for intervention. We have cloned, sequenced, and expressed a Cryptosporidium gene, Cpgp40/15 which encodes a major surface glycoprotein, gp40.15.

This glycoprotein is processed into two glycopeptides, gp40 and gp15 which are implicated in mediating 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 elucidating the molecular basis for the interaction of gp40 and gp15 with host cells, and on characterization of the post-translational processing and modifications of gp40/15 and its products, which may facilitate the identification of novel biochemical targets for future drug discovery. We are also investigating polypeptide-N-acetylgalactosaminyl transferases and subtilisin-like proteases which are involved in glycosylation and proteolytic processing of mucin-like glycoproteins such as gp40/15. These enzymes may also serve as putative drug targets.

We have also cloned and characterized a galactose - and N-acetyl-galactosamine - (Gal/GalNAc)-specific sporozoite lectin (i.e., a carbohydrate binding protein), named Cp30 which binds to Gal/GalNAc–containing glycoconjugates such as mucins and mucin-like proteins on the host as well as the parasite. Mucins, as well as oligosaccharides derived from them block attachment and subsequent infection of the parasite in vitro. This raises the possibility that mucin-derived oligosaccharide moieties may be used as preventive or interventional therapy against cryptosporidiosis in vivo. As an extension of these studies we showed that Cryptosporidium sporozoites themselves express Gal/GalNAc-containing mucin-like surface glycoproteins such as gp40 and gp15 , which are also implicated in attachment and invasion. Current studies are directed at determining the role of parasite and host lectins and mucin oligosaccharides in host-parasite interactions.

Immune Responses to and Molecular Epidemiology of Cryptosporidiosis

In collaboration with investigators in India , we are participating in longitudinal studies of cryptosporidiosis in well-defined populations of children and adults with and without HIV infection. In this area, cryptosporidiosis is the most common cause of parasitic diarrhea. We are investigating systemic and mucosal Cryptosporidium -specific humoral and cell-mediated immune responses in these individuals, performing multi-locus genotypic analysis of Cryptosporidium isolates from them and correlating genetic information with clinical epidemiological and immunological parameters. Single nucleotide polymorphisms in the Cpgp40/15 locus are being used to fingerprint isolates to identify the source and mode of transmission of Cryptosporidium infection. The long term goal of these studies is the logical development of interventions that are appropriate to the communities in which cryptosporidiosis is common.

Innate immune responses to C. parvum in mice

Innate immune responses are critical in resistance to C. parvum infection. However, the nature of these responses and the mechanisms by which the host recognizes the parasite and activates these responses are poorly understood. We have shown that mice deficient in MyD88 (an adaptor protein which mediates signaling by most of the Toll-like receptor pathways) are more susceptible to C. parvum than wild-type litter-mates. Current studies are directed at determining which Toll-like receptor s are involved in innate immune responses to C. parvum in human and murine cell lines in vitro as well as in mice in vivo and at identifying the ligands and specific signaling pathways involved. The long-term goal is to determine whether specific molecules or pathways can be targeted to enhance innate immunity to the parasite or to prevent immunopathology induced by dysregulated innate immune responses.