title: Phospholipid transmethylation in human mononuclear cells is not influenced by mitogens.
abstract: The importance of accelerated methyl transfer from methionine to membrane phospholipid (PL) as an early event in lymphocyte activation is vigorously debated. We have examined pokeweed mitogen (PWM)- and phytohemagglutinin (PHA)-stimulated human peripheral blood lymphocytes for this early activation event. Without mitogen, methyl groups rapidly entered into the PL of unfractionated human lymphocytes by 10 min, and then adopted a rate which stayed constant for at least 2 hr. Whether or not mitogen was added after a 60-min preincubation, with [3H]methyl methionine, after a further 20 min, Sephadex G-10 adherent monocytes were incorporating methyl groups into PL 4 times faster than B-cells and 9 times faster than T-cells. At 10(7) cells/ml, neither PWM nor PHA changed total PL labeling kinetics, or produced a significant change of methyl groups from phosphatidyl-N-mono- and dimethylethanolamine to phosphatidylcholine or lysophosphatidylcholine in B-cells, T-cells or monocytes, whether these populations were cultured separately or together. Even for the slowly incorporating human T-cells, the background rate of methyl transfer per cell was much greater than that previously reported for mouse or pig mononuclear cells. Accelerated methylation of phospholipid appears not to be a favorable early event by which to study human lymphocyte activation, and we agree with Moore et al. [J. biol. Chem. 257, 8183-8189 (1982)] that it may not be a universal activation event.
mesh_terms: D002450:Cell Communication; D002478:Cells, Cultured; D006801:Humans; D007700:Kinetics; D008213:Lymphocyte Activation; D008214:Lymphocytes / Q000378:metabolism*; D008715:Methionine; D008745:Methylation; D010743:Phospholipids / Q000097:blood*; D010835:Phytohemagglutinins / Q000494:pharmacology*; D011043:Pokeweed Mitogens / Q000494:pharmacology*
chemical_list: D010743:Phospholipids; D010835:Phytohemagglutinins; D011043:Pokeweed Mitogens; D008715:Methionine