Signaling lymphocyte activating molecule (SLAM) is a receptor for measles virus which also has immunomodulatory activity. We analyzed SLAM expression in mononuclear cells (MNC) of patients with SSPE (n = 7) and control subjects (n = 7) from the same population. Native 10% PAGE analysis in cell and brain tissue extracts followed by Western blotting using monoclonal anti-human SLAM showed four types of bands. Differences in the type and amount of SLAM expression were observed between SSPE and control cases. Lymphocytes of SSPE patients showed two types of SLAM bands in comparison to only one in control lymphocytes. Stimulation of cells with lipopolysaccharide (80 u/ml) and concanavalin A (1 mu g/ml) in vitro led to the appearance of a second isoform in both groups. Brain homogenates of SSPE patients (n = 2) displayed all four types of SLAM isoforms at significantly higher levels than those of control brains (n = 2). Our results show native PAGE enables the detection of all SLAM isotypes. The expression of SLAM is increased in lymphocytes, monocytes, and brain tissues of SSPE patients. (c) 2006 Elsevier B.V. All rights reserved.