Published online before print January 22, 2007

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(Journal of Leukocyte Biology. 2007;81:1002-1011.)
© 2007 by Society for Leukocyte Biology

Glycosylation-dependent interaction of Jacalin with CD45 induces T lymphocyte activation and Th1/Th2 cytokine secretion

Makoto Baba^*,,1, Bruce Yong Ma^*,1,2, Motohiro Nonaka^*,, Yukari Matsuishi, Makoto Hirano^*,, Natsuko Nakamura^*,, Nana Kawasaki, Nobuko Kawasaki^* and Toshisuke Kawasaki^*,2

^* Research Center for Glycobiotechnology, Ritsumeikan University, Shiga, Japan;
Department of Biological Chemistry, Graduate School of Pharmaceutical Sciences, Kyoto University, Kyoto, Japan; and
Division of Biological Chemistry and Biologicals, National Institute of Health Sciences, Tokyo, Japan

² Correspondence: Research Center for Glycobiotechnology, Ritsumeikan University, Shiga 525-8577, Japan. E-mail: byma{at}fc.ritsumei.ac.jp; tkawasaki{at}fc.ritsumei.ac.jp

Jacalin, an -O-glycoside of the disaccharide Thomsen-Friedenreich antigen (galactose ß1-3 N-acetylgalactosamine, T-antigen)-specific lectin from jackfruit seeds, has been shown to induce mitogenic responses and to block infection by HIV-1 in CD4⁺ T lymphocytes. The molecular mechanism underlying Jacalin-induced T cell activation has not been elucidated completely yet. In the present study, protein tyrosine phosphatase (PTPase) CD45 was isolated from a Jurkat T cell membrane fraction as a major receptor for Jacalin through affinity chromatography and mass spectrometry. CD45, which is highly glycosylated and expressed exclusively on the surface of lymphocytes, is a key regulator of lymphocyte signaling, playing a pivotal role in activation and development. We found that the lectin induced significant IL-2 production by a CD45-positive Jurkat T cell line (JE6.1) and primary T cells. However, this effect did not occur in a CD45-negative Jurkat T cell line (J45.01) and was blocked completely by a specific CD45 PTPase inhibitor in Jurkat T (JE6.1) and primary T cells. Furthermore, we also observed that Jacalin caused a marked increase in IL-2 secretion in response to TCR ligation and CD28 costimulation and contributed to Th1/Th2 cytokine production by activating CD45. Jacalin increased CD45 tyrosine phosphatase activity, which resulted in activation of the ERK1/2 and p38 MAPK cascades. Based on these findings, we propose a new, immunoregulatory model for Jacalin, wherein glycosylation-dependent interactions of Jacalin with CD45 on T cells elevate TCR-mediated signaling, which thereby up-regulate T cell activation thresholds and Th1/Th2 cytokine secretion.

Key Words: carbohydrate recognition • lectin-carbohydrate interaction • protein-tyrosine phosphatases • protein-tyrosine kinase

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