Anti-Trypanosoma brucei activity in Cape buffalo serum during the cryptic phase of parasitemia is mediated by antibodies

• Published in: International journal for parasitology 2007-10, Vol.37 (12), p.1391-1399
• Main Authors: Guirnalda, Patrick, Murphy, Noel B., Nolan, Derek, Black, Samuel J.
• Format: Article
• Language: English
• Subjects: Animals; Antibodies, Protozoan - blood; Antibodies, Protozoan - immunology; Antibody; antibody formation; Antibody Specificity; antigen-antibody reactions; antiserum; Biological and medical sciences; Buffaloes - blood; Buffaloes - parasitology; Cape buffalo; Cattle; cryptic infection; Cryptic phase; disease reservoirs; Fundamental and applied biological sciences. Psychology; immune response; immunoglobulin G; immunoglobulin M; Life cycle. Host-agent relationship. Pathogenesis; Lycopersicon esculentum; Mammalia; parasitemia; Parasitemia - immunology; Protozoa; Statistics as Topic; Syncerus caffer; Tomato lectin; Trypanosoma; Trypanosoma brucei; Trypanosoma brucei brucei - immunology; trypanosome growth; trypanosomiasis; Trypanosomiasis, Bovine - immunology; variant surface glycoproteins; Vertebrates: general zoology, morphology, phylogeny, systematics, cytogenetics, geographical distribution
• ISSN: 0020-7519; 1879-0135
• DOI: 10.1016/j.ijpara.2007.04.019

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.