Stimulation of human peripheral blood lymphocytes by procaryotic ribosomal proteins isolated from bacterium E. coli

Abstract

The total protein fractions (TP) isolated from bacterium Escherichia coli ribosomal 50S and 30S subunits were found to be the mitogenic components of E. coli ribosomes triggering DNA synthesis of human peripheral and cord blood lymphocytes. Stimulation parameters including kinetics and dose—response curves of TP 50-induced lymphocyte stimulation are demonstrated. It could further be shown that all individual proteins (28 of the 32 proteins present in the total protein fraction of 50 S were tested) induced a significant proliferative response. The magnitude of the responses, however, differed considerably and could be correlated to the molecular weight of the single ribosomal proteins. Furthermore, it was shown that ribosomal proteins isolated from Bacillus stearothermophilus, which is not part of the human intestinal flora, are mitogenic for human peripheral lymphocytes as well. Proteins isolated from eucaryotic ribosomes (from human, mice, and rat liver), on the other hand, were unable to induce a DNA synthetic response. T lymphocytes were identified as the target cells, whereas B cells did not respond significantly as measured by DNA synthesis. However, a significant polyclonal B-cell activation could be demonstrated using a reverse hemolytic plaque assay. This activation required a 10-fold higher concentration of TP 50 than that found to be optimal for the proliferative response of T lymphocytes.