Induction of lymphocyte proliferation and membrane changes by lipopeptide derivatives of the lipoprotein from the outer membrane of Escherichia coli

Abstract

Lipoprotein from the outer membrane of E. coli, a potent novel mitogen, was digested by pronase treatment resulting in lipopeptide fragments containing 2-5 amino acids bound to diacylglyceryl-N-acylcysteinthioether. The lipopeptides were characterized by amino acid analysis and gas chromatography and were checked for mitogenicity. We found that all lipopeptide fragments were able to stimulate the uptake of 3H-uridine into RNA and 3H-thymidine into DNA in mouse spleen cells of several strains. The response of splenocytes of congenitally athymic mice was comparable to that of normal animals. A weak stimulation of DNA synthesis was also observed in thymocytes. The mitogenicity of the products was abolished by mild alkali hydrolysis which removes the ester-bound fatty acids. We conclude that the N-terminal lipopeptide region of lipoprotein is responsible for the mitogenic activity of the molecule. Lipopeptide as well as lipoprotein were found to cause early membrane changes in lymphocyte plasma membranes. After 4 hours we found an increased incorporation of 14C-oleate and 14C-acetate into lecithin. The membrane changes observed are similar to those brought about by mitogenic lectins, which suggests a similar mechanism for the induction of lymphocyte activation for both types of mitogens.