Chris received his M.D. degree in 1994 from Cornell University Medical College. He then served as an intern, resident, and chief resident in internal medicine at the University of Vermont. From 1998 to 2000, he was a fellow in infectious diseases at the University of Virginia, after which he received a Howard Hughes Postdoctoral Fellowship to continue his training. He joined UVM’s infectious diseases faculty in 2003.

Research Interests

In our laboratory we study two waterborne intestinal protozoa that infect humans: Entamoeba histolytica and Cryptosporidium parvum. Both of these parasites are major public health problems in the developing world. They predominantly affect young children and, in the case of Cryptosporidium, immunocompromised individuals such as those with AIDS. Recently, both have garnered increasing interest in the United States due to concern that they could be intentionally introduced into the water supply in an act of bioterrorism.

Entamoeba histolytica, the cause of amebic dysentery and liver abscess, infects an estimated 50 million people annually. The ability of E. histolytica to kill and phagocytose host cells correlates with parasite virulence. In fact, phagocytosis of host erythrocytes is the only feature on light microscopy that distinguishes E. histolytica from the non-pathogenic intestinal ameba Entamoeba dispar, a feature used for clinical diagnosis. As a precursor to defining the roles amebic cell killing and phagocytic ability play in pathogenesis, this project’s goal is to delineate the molecular mechanisms underlying these processes. For this we are using flow cytometry and microscopy-based phagocytosis assays, confocal microscopy to localize epitope-tagged recombinant proteins, and a variety of biochemical and molecular techniques. Our studies have shown that E. histolytica kills host cells by inducing apoptosis, and ingests apoptotic cells more efficiently than healthy or necrotic cells. Furthermore, inhibition of the major amebic surface adhesin, which completely blocks adherence and cell killing, does not prevent ingestion of apoptotic cells, implicating at least one additional receptor in the recognition and clearance of killed cells. By purifying amebic phagosomes and using mass spectrometry, several candidate phagocytosis receptors have been identified and these proteins are currently being characterized. These studies promise to yield a greater understanding of how E. histolytica causes disease and may suggest improved methods for treatment and prevention of amebiasis.

Cryptosporidium species cause severe diarrhea in both immunocompetent and immunocompromised individuals. The infectious oocysts are resistant to standard water treatment methods and Cryptosporidium has been associated with numerous waterborne epidemics including one involving more than 400,000 Milwaukee residents in 1993. Nitazoxanide is the only available treatment for cryptosporidiosis, but it is ineffective for immunocompromised patients in whom infection can be fatal. Though new drugs are badly needed, drug development has been impeded by an inability to continuously culture the parasite in vitro. Within the host Cryptosporidium is dependent on anaerobic metabolism, making its fermentation enzymes attractive drug targets. Our preliminary studies indicate that a bifunctional acetaldehyde-alcohol dehydrogenase E (CpAdhE) catalyzes two terminal fermentation reactions. The AdhE enzymes are structurally distinct from human dehydrogenases, and contain separate acetaldehyde and alcohol NAD+-dependent dehydrogenase domains. Many gram-negative and gram-positive bacteria as well as several intestinal protozoa have AdhE enzymes, and an AdhE is essential for anaerobic growth of Eschericia coli. In this work, we are using a transgenic model to circumvent the need to cultivate Cryptosporidium and validate AdhE as a drug target for cryptosporidiosis. Genetic complementation of an E. coli AdhE mutant with recombinant CpAdhE and assays for restoration of anaerobic growth are being used to verify the function of CpAdhE. To assay NAD+-dependent aldehyde and alcohol dehydrogenase activities in bacterial lysates, a spectrophotometer is used to follow reduction of NAD+ to NADH. The long-term goal of this project is to use this spectrophotometric assay to conduct a small molecule screen for CpAdhE inhibitors. Cryptosporidium parvum’s dependence on CpAdhE for growth and development will be determined using an assay for C. parvum development in tissue culture. We expect these studies to yield important data on Cryptosporidium metabolism and to identify compounds that may be useful for treatment of this deadly parasitic infection.

Model of sequential cell killing and phagocytosis by E. histolytica

E. histolytica (green) ingests apoptotic (B) but not viable (A) Jurkat lymphocytes (red).

Selected Publications

Vincent MS, Roessner K, Sellati T, Huston CD, Sigal LH, Behar SM, Radolf JD, Budd RC. Lyme arthritis synovial gamma-delta T cells respond to Borrelia burgdorferi lipoproteins and lipidated hexapeptides. Journal of Immunology. 1998. 161:5762-5771.

Huston CD, Petri WA. Host-pathogen interaction in amebiasis and progress in vaccine development. European Journal of Clinical Microbiology and Infectious Diseases. 1998. 17:601-614.

Huston CD, Petri WA. Amebiasis: clinical implications of the recognition of Entamoeba dispar. Current Infectious Disease Reports. 1999. 1:441-447.

Huston CD, Houpt ER, Mann BJ, Hahn CS, Petri WA. Caspase 3-dependent killing of host cells by the parasite Entamoeba histolytica. Cellular Microbiology. 2000. 2:617-625.

Cheng XJ, Hughes MA, Huston CD, Loftus BB, Gilchrist CA, Lockhart LA, Ghosh S, Miller-Sims V, Mann BJ, Petri WA, Tachibana H. Intermediate subunit of the Gal/GalNAc lectin of Entamoeba histolytica is a member of a gene family containing multiple CXXC motifs. Infection and Immunity. 2001. 69:5892-5898.

Haque R, Huston CD, Hughes M, Houpt E, Petri WA. Current Concepts: Amebiasis. New England Journal of Medicine. 2003. 348:1565-1573.

Huston CD, Boettner DR, Miller-Sims V, Petri WA. Apoptotic killing and phagocytosis of host cells by the parasite Entamoeba histolytica. Infection and Immunity. 2003. 71: 964-972.

Huston CD. Parasite and host contributions to the pathogenesis of amebic colitis. Trends in Parasitology. 2004. 20:23-26.

Boettner DR, Huston CD, Sullivan J, Petri WA. Entamoeba histolytica and Entamoeba dispar utilize externalized phosphatidylserine for recognition and phagocytosis of erythrocytes. Infection and Immunity. 2005. 73:3422-3430.

Okada M, Huston CD, Mann BJ, Petri WA, Kita K, Nozaki T. Comprehensive proteomics analysis of phagocytosis by the enteric protozoan parasite Entamoeba histolytica. Eukaryotic Cell. 2005. 4:827-831.

Okada M, Huston CD, Oue M, Mann BJ, Petri WA, Kita K, Nozaki T. Kinetics and strain variation of phagosome proteins of Entamoeba histolytica by proteomic analysis. Molecular and Biochemical Parasitology. 2006. 145:171-83. Molecular and Biochemical Parasitology. 2006. 145:171-83.

Huston CD, Miller-Sims VC, Teixeira JE. Identification and characterization of EhABC A1, an Entamoeba histolytica group A ABC transporter with similarity to Ced7. Molecular and Biochemical Parasitology. 2006. 146:272-6. Molecular and Biochemical Parasitology. 2006. 146:272-6.

Kirkpatrick BD, Huston CD, Wagner D, Noel F, Rouzier P, Pape JW, Bois G, Larsson CJ, Alston WK, Tenney K, Powden C, O\'Neill JP, Sears CL. Serum mannose-binding lectin deficiency is associated with cryptosporidiosis in young Haitian children. Clinical Infectious Diseases. 2006. 43:289-94. Clinical Infectious Diseases. 2006. 43:289-94.

Boettner DR, Huston CD, Linford AS, Buss SN, Houpt E, Sherman NE, Petri WA. Entamoeba histolytica phagocytosis of human erythrocytes involves PATMK, a member of the transmembrane kinase family. PLoS Pathogens. 2008. 4(1):122-33. PMID: 18208324.

Teixeira JE, Huston CD. Participation of the serine-rich Entamoeba histolytica protein in amebic phagocytosis of apoptotic host cells. Infection and Immunity. 2008. 76:959-66. PMID: 18086807.

Teixeira JE, Huston CD. Evidence of a continuous endoplasmic reticulum in the protozoan parasite Entamoeba histolytica. Eukaryotic Cell. 2008. 7:1222-1226. PMID: 18281599. [includes cover photo]

Teixeira JE, Heron BT, Huston CD. C1q- and collectin-dependent phagocytosis of apoptotic host cells by the intestinal protozoan Entamoeba histolytica. Journal of Infectious Diseases. 2008. 198:1062-1070. PMID: 18702607.

CMB Lab Members