Molecular and Biochemical Parasitology 111 (2000) 333 – 349 The major cell surface glycoprotein procyclin is a receptor for induction of a novel form of cell death in African trypanosomes in vitro Terry W. Pearson a,e, *, Robert P. Beecroft a , Susan C. Welburn b,e , Stefan Ruepp c , Isabel Roditi c , Kuo-Yuan Hwa d,1 , Paul T. Englund d , Clive W. Wells e , Noel B. Murphy e a Department of Biochemistry and Microbiology, Petch Building, Uniersity of Victoria, P.O. Box 3055, Victoria, BC, Canada V8W 3P6 b Vector Research Group, Centre for Tropical Veterinary Medicine, Royal Dick School of Veterinary Medicine, Uniersity of Edinburgh, Roslin, Midlothian EH25 9RG, Scotland, UK c Institut fu ¨r Allgemeine Mikrobiologie, Uniersita ¨t Bern, Baltzerstrasse 4, CH-3012 Bern, Switzerland d Department of Biological Chemistry, Johns Hopkins School of Medicine, Baltimore, MD 21205 -2185, USA e International Liestock Research Institute, P.O. Box 30709, Nairobi, Kenya Received 8 May 2349; received in revised form 21 August 2000; accepted 21 August 2000 Abstract Bloodstream forms (BSF) and procyclic culture forms (PCF) of African trypanosomes were incubated with a variety of lectins in vitro. Cessation of cell division and profound morphological changes were seen in procyclic forms but not in BSF after incubation with concanavalin A (Con A), wheat germ agglutinin and Ricinus communis agglutinin. These lectins caused the trypanosomes to cease division, become round and increase dramatically in size, the latter being partially attributable to the formation of what appeared to be a large ‘vacuole-like structure’ or an expanded flagellar pocket. Con A was used in all further experiments. Spectrophotometric quantitation of extracted DNA and flow cytometry using the DNA intercalating dye propidium iodide showed that the DNA content of Con A-treated trypanosomes increased dramatically when compared to untreated parasites. Examination of these cells by fluorescence microscopy showed that many of the Con A-treated cells were multinucleate whereas the kinetoplasts were mostly present as single copies, indicating a disequilibrium between nuclear and kinetoplast replication. Immunofluorescence experiments using monoclonal antibodies (mAb) specific for paraflagellar rod proteins and for www.parasitology-online.com. Abbreiations: BSF, bloodstream forms; Con A, concanavalin A; DAPI, 46-diamidino-2-phenylindole; ELISA, enzyme-linked immunosorbent assay; GARP, glutamic acid/alanine-rich protein; KMP-11, kinetoplastid membrane protein-11; mAb, monoclonal antibodies; PCF, procyclic culture forms; SDS-PAGE, sodium dodecylsulfate polyacrylamide gel electrophoresis; TUNEL, terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling; VSG, variant surface glycoprotein. * Corresponding author. Tel.: +1-250-7217080; fax: +1-250-7218855. E-mail address: parasite@uvvm.uvic.ca (T.W. Pearson). 1 Present address: Institute of Biological Chemistry, Academia Sinica, 128 Yen-Gio Yuan Road, Taipei 115, Taiwan, R.O.C. 0166-6851/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII:S0166-6851(00)00327-3