DIFFERENCES BETWEEN B-CELL AND MACROPHAGE TRANSFORMATION BY THE BOVINE PARASITE, THEILERIA-ANNULATA - A CLONAL APPROACH

Theileria annulata, a tick-transmitted protozoan parasite, infects and transforms cells of the hemopoietic system, particularly those of the B cell and monocyte/macrophage lineages. Here, the effect of infectio n/transformation on the resulting phenotype was studied using a clonal approach. Three phenotypes of transformed cell lines could be discern ed. The first is characterized by surface expression of IgM, CD21, and the B cell epitopes, B-B2 and B-B8, Ig heavy chain gene rearrangement , and mRNA expression. Such lines were obtained from fresh and culture d PBMC and at increased frequency from purified B cells, but never fro m fetal bone marrow cells. The second phenotype can be distinguished f rom the first by the absence of Ig heavy chain expression and reduced surface expression of B cell markers (CD21, B-B2, B-B8), Clones with t his phenotype were obtained from transformed fetal bone marrow cells o nly, The third phenotype showed an absence of all of the above B cell markers, including surface IgM, and a lack of Ig heavy chain gene rear rangement. The latter clones could be maintained for several weeks aft er elimination of T. annulata by BW720c treatment, and they reacquired a macrophage-like phenotype, This implies that parasite-induced dedif ferentiation is restricted to monocyte/macrophage, and that B cell mar kers are indicative of cell lineage progeny. Demonstration of surface IgM on PBMC-derived B cell clones suggests that infection of B cells w ith T. annulata may be an epigenetic method to immortalize ruminant B cells of a defined Ag specificity.