Expression and characterization of the interleukin 2 receptor in Theileria parva-infected bovine lymphocytes.

We have previously shown that interleukin 2 receptors (IL2R) are constitutively expressed on the surface of bovine lymphocytes infected with the parasite Theileria parva (Dobbelaere, D.A.E. et al., Proc. Natl. Acad. Sci. USA 1988. 85: 4730). In the present work we characterized these further and showed that IL2R (Tac antigen) gene expression depended on the continuous presence of the parasite in the host cell cytoplasm. By Northern blot analysis we showed that elimination of the parasite, using a specific theilericidal drug, led to the arrest of Tac antigen mRNA expression. We also investigated receptor internalization and reappearance after receptor-mediated endocytosis. Binding of human recombinant interleukin 2 (hrIL2) to the bovine IL2R caused rapid internalization of the surface IL2/IL2R complex. Approximately 50% of 125I-labeled hrIL2 was internalized within 10 min. The reappearance of surface IL2R after ligand-mediated endocytosis was also studied. Fifty percent of the maximum level of free IL2R reappeared within 1-1.5 h, but approximately 12 h were needed to restore normal levels of free IL2R expression after blocking with excess unlabeled hrIL2.