Calcium-Dependent Homotypic Adhesion Through Leukocyte Function-Associated Antigen-l/Intracellular Adhesion Molecule-l Induces Interleukin-l and Parathyroid Hormone-Related Protein Production on Adult T-cell Leukemia Cells In Vitro

Adutt T-cell leukemia (ATL) is a human T-cell leukemia virus type I (HTLV-l)-infected lymphoproliferative disorder that shows a characteristic nodular infiltration into various tissues, hypercalcemia, and subsequent rapid increase of peripheral ATL cell number. ATL cells and HTLV-l-infected T-cell lines also make cluster formation rapidly after the nonstimulative culture. However, the mechanism of the acute proliferation of ATL cells remains to be understood. We report the following novel features of homotypic adhesion via leukocyte function-associated antigen-l (LFA-1)lintracellular adhesion molecule-l (ICAM-1) pathway that suggest a role for it in cytokine production and rapid proliieration of ATL cells: (1) ATL cells show clustering in a calcium dependent manner, even at the higher concentration; (2) ATL cells consistently and highly express ICAM-1 and an active form of LFA-1, whereas integrin expression, except for LFA-1, is rather lower compared with that of normal CD4+ T cells; (3)