title: Anti-Trypanosoma brucei activity in Cape buffalo serum during the cryptic phase of parasitemia is mediated by antibodies.
abstract: Cape buffalo are reservoir hosts of African trypanosomes. They rapidly suppress population growth of the highly antigenically variable extracellular haemoprotozoa and subsequently maintain a cryptic infection. Here we use in vitro cultures of trypanosomes cloned from Cape buffalo blood during cryptic infection, as well as related and unrelated trypanosomes, to identify anti-trypanosome components present in cryptic-phase infection serum. Trypanosome clone-specific complement-dependent trypanolytic IgM and IgG arose after appearance of target trypanosomes during cryptic infection. Serum collected late in the cryptic phase of infection contained complement-independent growth-inhibitory IgG which varied in activity among target trypanosomes. Removal of protein A/G-binding IgG from the serum restored its capacity to support trypanosome growth in vitro. Recovered growth-inhibitory IgG reacted with the variable surface glycoprotein (VSG) of parasites most affected by it, and reacted with trypanosome common antigens, notably the endosome-restricted tomato lectin-binding glycoproteins (TL-antigens). The inclusion of purified TL-antigens in culture medium did not affect the trypanosome growth-inhibitory activity of immune Cape buffalo serum. In addition, hyperimmune rabbit IgG against TL-antigens showed little or no binding to intact trypanosomes and did not affect trypanosome growth in vitro although it did react strongly with TL-antigens and trypanosome endosomes. We conclude that antibodies, particularly clone-specific (putatively VSG-specific) antibodies are responsible for the anti-trypanosome activity of cryptic phase infection serum consistent with a dominant role in parasite control in Cape buffalo.
authors.affiliation: Department of Veterinary and Animal Sciences, University of Massachusetts, Amherst, MA 01003, USA.
authors.forename: Patrick
authors.initials: P
authors.lastname: Guirnalda
authors.forename: Noel B
authors.initials: NB
authors.lastname: Murphy
authors.forename: Derek
authors.initials: D
authors.lastname: Nolan
authors.forename: Samuel J
authors.initials: SJ
authors.lastname: Black
mesh_terms: D000818:Animals; D000913:Antibodies, Protozoan / Q000097:blood / Q000276:immunology*; D000918:Antibody Specificity; D002020:Buffaloes / Q000097:blood / Q000469:parasitology*; D002417:Cattle; D018512:Parasitemia / Q000276:immunology*; D013223:Statistics as Topic; D014346:Trypanosoma brucei brucei / Q000276:immunology*; D014354:Trypanosomiasis, Bovine / Q000276:immunology*
chemical_list: D000913:Antibodies, Protozoan