The Establishment Of VSG Antigenic Reservoir Of Trypanosome Evansi And Its Detection Of Protective Immunity

Trypanosome escapes the immune reaction of host due to changing its' variable surface glycoprotein (VSG). VSG is commonly considered a strong immunogen and only enables the immune protection to homotype rather than heterotype. Mass proliferation of Trypanosome results in a weakness and death of host. The studies have showed that the variant antigen type (VAT) known as predominant variant antigen type (VAT) is limited in early infection; however, a high repetition can be seen and reaches 60%. In order to inhibit the variation and second variation of Trypanosome, a predominant VSG antigenic reservoir has been established by purification VSG from VAT, leading to a better immune protection and overcome immune failure due to antigenic variation. According to the characteristics that Trypanosome can produce different variations, 5 New Zealand rabbits were infected in sequence with a monoclonal strain of Trypanosome evansi isolated from Yunnan buffalo. 50 monoclonal strains were isolated and showed by indirect immune fluorescent test that the first parasitemia peak of variation in following 4 rabbits exist in 9 predominant variations of first rabbit. The 50 variations subordinate to 20 antigen types. All predominant variation VSG was purified to set up antigenic reservoir. Experimental mice were exposed to Trypanosome evansi after injection by different doses of antigenic reservoir. The results showed that 20 μg dose produced 83% and 67% protection to 2 sample variations after 4 immunizations. However, 3 immunizing doses could not give good protection. No protective effects were detected when experimental animals immunized by single VSG exposed to isotype from different rabbits. The antigenic reservoir produced a protective rate as high as 80%, which provides a way for developing new vaccine of Trypanosome evansi.