THEILERIA-ANNULATA - THE EXPRESSION OF 2 NOVEL MACROSHIZONT ANTIGENS ON THE SURFACE OF INFECTED MONONUCLEAR-CELLS DIFFERS DURING IN-VITRO ATTENUATION OF A VIRULENT CELL-LINE

The first part of this study of the biology Cal mechanisms underlying attenuation of virulent Theileria annulata macroschizont-infected cell Lines screened four pairs of T. annulata (Hisar) in vivo- and in vitr o-derived macroschizont-infected cell Lines (lines) and identified a s ingle in vivo-derived line, which induced lethal tropical theileriosis . The other seven lines were relatively avirulent. Analysis of the cli nical, hematological, and parasitological responses of cattle immunize d with different passages of the virulent line after in vitro culture showed that it was partly attenuated by passage (p) 50 and avirulent b y p130. Clones representing the three glucose phosphate isomerase (GPI ) isotypes, which constituted the newly isolated virulent culture, wer e obtained from p3 by limiting dilution: p50 and p130 consisted of one isotype. The second part of the study raised monoclonal antibodies (M Abs) against macroschizont-infected cells, as reagents for detecting a ntigenic differences between virulent and avirulent parasites, and ide ntified two MAbs that recognized the surface of infected cells as well as macroschizonts, MAb EU1 recognized an antigen expressed by all the lines tested, whether in vitro- or in vivo-derived, whether uncloned or cloned, and irrespective of extent of subpassage in culture. MAb EU 106 recognized an antigen whose expression by the virulent line and it s clones disappeared on passage in culture. This antigen was not expre ssed at all by the avirulent iir vitro-derived line prepared with cell s from the same calf Both antigens were expressed by lines infected wi th other stocks of T. annulata, including two lines known to induce le thal disease. The different profiles of expression of the two novel an tigens, recognized by MAbs EU1 and EU106, by the line undergoing atten uation suggest (1) that the two antigens interact differently with the bovine immune system; and (2) that there are two, very different, pot ential roles for these antibodies in the development of vaccines again st T. annulata infections. (C) 1998 Academic Press.