| Abstract: | Lipoprotein from the outer membrane of Escherichia coli and a synthetic analogue of its N-terminal lipopeptide part, tripalmitoyl-pentapeptide, constitute potent mitogens and polyclonal activators of murine B-lymphocytes in vitro. When entering the circulation after intravenous administration in experimental animals, they interact with the humoral and cellular elements of the blood, which results in splenomegaly and B-lymphocyte activation in vivo. We investigated lipopeptide-binding proteins in normal mouse serum and on splenocytes. By affinity chromatography using an affinity adsorbent prepared by coupling the lipoprotein analogue to CPG-aminopropyl derivatized glass beads, we could enrich one major binding protein for tripalmitoyl-pentapeptide from mouse serum, which was identified as albumin. Binding proteins on lymphocytes were determined as follows: Spleen cells of C3H/HeJ mice were activated by the B cell mitogen lipoprotein, biosynthetically labelled with 3H]leucine, and solubilized by the nonionic detergent Nonidet P40. From the cell lysate, binding proteins were isolated by affinity chromatography: As analysed by polyacrylamide gel electrophoresis and autoradiography, proteins with molecular masses of 24, 27, 33, 45, 53, 61 and 71 kDa were eluted from the tripalmitoyl-pentapeptide adsorbent. The eluted material was further enriched for glycoproteins by Lens culinaris lectin affinity chromatography, and immunoprecipitation studies were performed with the glycoprotein fractions using alloantisera specific for class I and class II gene products of the H-2k haplotype. We could show that both class I and class II MHC glycoproteins could be enriched on the tripalmitoyl-pentapeptide column. This finding might suggest that, among other proteins, MHC-encoded proteins are involved in lymphocyte activation by a mitogenic lipopeptide. |
