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

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Abstract
We have previously shown that interleukin 2 receptors (IL 2R) 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 IL 2R (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 (hrIL 2) to the bovine IL 2R caused rapid internalization of the surface IL 2/IL 2R complex. Approximately 50% of 125I-labeled hrIL 2 was internalized within 10 min. The reappearance of surface IL 2R after ligand-mediated endocytosis was also studied. Fifty percent of the maximum level of free IL 2R reappeared within 1–1.5 h, but approximately 12 h were needed to restore normal levels of free IL 2R expression after blocking with excess unlabeled hrIL 2.