ALZHEIMERS AMYLOID PRECURSOR PROTEIN IS EXPRESSED ON THE SURFACE OF HEMATOPOIETIC-CELLS UPON ACTIVATION

A4-amyloid is the major component pc senile plaques and neurofibrillar y tangles found in the brain of patients suffering Alzheimer's disease . This 39-42 amino acid peptide is derived from a larger precursor pro tein (APP). Since APP gene encodes for a putative memebrane protein, t he study of APP expression at the cell surface may provide useful data for understanding its physiological function. In this report, we pres ent data on APP expression, that was detected by APP specific mAbs in cells of the hematopoietic system. APP was weakly expressed on the cel l surface of resting human lymphocytes and monocytes, but it could be induced to the surface of those cells upon stimulation. The cell activ ators capable of inducing APP membrane expression comprehended mitogen ic lectins, calcium ionophores, phosphatase inhibitors, and anti mu-ch ain or anti-CD3 antibodies in B and T cells, respectively. Interesting ly, phorbol esters were able to induce APP membrane expression in mono cytic, but not in lymphoid cells. In contrast to lymphocytes and monoc ytes, granulocytes never expressed cell surface or cytoplasmic APP, ev en after the activation. The induction of membrane APP in response to lymphocyte activation signals, including antibodies to the antigen rec eptor of B and T cells, raises the possibility that APP might play the role of a cell surface receptor in the immune system.