Bioscience Reports, Vol. 10, No. 1, 1990 Myelin Basic Protein Inhibits the Calcium Response to Phytohaemagglutinin in Human Lymphocytes Tiziana Bellini, Diana Degani, Maurizio Matteuzzi and Franco Dallocchio ~ Received August 2, 1989 Myelin Basic Protein, one of the major membrane protein component of the central nervous system, was used to probe the molecular mechanism of cellular activation by phytohaemagglutinin. Pre-treatment of human lymphocytes with myelin basic protein results in a lower rising of cytosolic concentration of free calcium after stimulation with phytohaemagglutinin. This effect is dependent on myelin basic protein concentration and on the preincubation time of the protein with the cells. It is not due to a interaction between myelin basic protein and phytohaemagglutinin, but appears to be a consequence of the binding of the protein to the cell surface. The reduction of the rise of cytosolic calcium induced by phytohaemagglutinin is specific for the myelin basic protein because other proteins like albumin and protamine have no effect. KEY WORDS: myelin basic protein; lymphocytes; phytohaemagglutinin; calcium. INTRODUCTION Myelin Basic Protein (MBP) is one of the most abundant proteins of the central nervous system myelin and its proposed physiological role is to maintain the compact structure of the myelin sheath through protein-membrane and protein- protein interactions. A special consideration has been focused on the im- munological properties of this protein (1, 2), which induces in experimental animals a T cells mediated experimental autoimmune encephalomyelitis (3). In several demyelinating deseases MBP is released in the cerebro spinal fluid, and could be recognized by the immune system: this raises the question on the role of this protein on the evolution of demyelinating pathologies. To get more information on this problem we have investigated the action of MBP on human lymphocytes. t To whom correspondence should be addressed: Istituto di Chimica Biologica, Universita' di Ferrara, via L. Borsari 46, 44100 Ferrara, Italy. 55 0144-8463/90t0"200-0055505.00/0 ~ 1990 Plenum Publishing Corporation