BLT-esterase in infectious mononucleosis.

Peripheral blood lymphocytes of three patients suffering from infectious mononucleosis due to Epstein-Barr virus (EBV) infection were analysed for BLT-esterase expression in peripheral blood lymphocytes by a well established cytochemical staining method. During the acute phase of disease with presence of clinical symptoms a very high level of up to 90% BLT-esterase-expressing lymphocytes were detected. The increased percentage of lymphocytes expressing BLT-esterase coincided with the time of greatest symptoms and the peak elevation of hepatocellular enzymes. The still moderately elevated level only gradually decreased to normal during the further recovery period of 2 months during which the patients described episodes of weakness. Peripheral blood lymphocyte phenotype analysis revealed a marked CD8 lymphocytosis, a CD4/CD8 ratio of about 0.2, low number of CD19+ B cells, and a high level of DR+ CD3+ lymphocytes. Reduction of BLT esterase expression during the recovery period coincided with reduction of CD8+ DR+ lymphocytes. By a combination of BLT-esterase staining with immunocytochemical phenotype analysis, 95% of CD8+ lymphocytes were found to be BLT-esterase-positive. BLT-esterase might be involved in the immunodefence against EBV in infectious mononucleosis by inducing apoptosis in EBV-transformed B cells.