CD2 triggering stimulates a phospholipase A2 activity beside the phospholipase C pathway in human T lymphocytes.
In previous studies we demonstrated the triggering of the phospholipase C (PLC) pathway during the activation of an Ag-specific human CD4+ T lymphocyte clone by a mitogenic pair of CD2 (X11,D66) mAb. Similar conditions were applied to investigate a possible involvement of a phospholipase A2 (PLA2) acting as an additional alternative pathway during human T cell activation. Our results show that arachidonic acid or its derivatives are released after CD2 triggering. This release is largely independent of PLC activation and is mediated by a PLA2 because: 1) phosphatidylcholine is the preferential source of [3H]arachidonate release; 2) [3H]arachidonic acid release and phosphatidylcholine hydrolysis are blocked by two inhibitors of solubilized PLA2, mepacrine, and 4-p-bromophenacylbromide; and 3) we evidenced a PLA2 activity in cell homogenates. Extracellular calcium appears to play a critical role because the effects of CD2 mAb were inhibited in a Ca2(+)-depleted medium. In contrast, protein kinase C is not implicated since PMA, a protein kinase C activator, neither stimulated arachidonic acid release nor modulated CD2-induced arachidonic acid release. Cyclic AMP which has been proved to regulate the activity of the PLC in T lymphocytes does not appear to play an important role in the regulation of PLA2 activity since PGE2 has only a minimal effect on [3H]-arachidonate release. Altogether, these findings suggest that CD2 triggering stimulates a PLA2 activity in T lymphocytes via an extracellular Ca2(+)-dependent PLC protein kinase C independent mechanism.
Le Gouvello
S
S
Laboratoire d'Immunologie Cellulaire et Tissulaire, CNRS UA 0186, Hopital de la Pitie-Salpetriere, Paris, France.
Colard
O
O
Theodorou
I
I
Bismuth
G
G
Tarantino
N
N
Debre
P
P
D000945:Antigens, Differentiation, T-Lymphocyte / Q000502:physiology*; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000378:metabolism; D018801:CD2 Antigens; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology / Q000502:physiology*; D002118:Calcium / Q000502:physiology; D002999:Clone Cells; D000242:Cyclic AMP / Q000378:metabolism; D003512:Cyclohexanones / Q000494:pharmacology; D004789:Enzyme Activation; D006801:Humans; D066298:In Vitro Techniques; D008071:Lipoprotein Lipase / Q000037:antagonists & inhibitors; D008213:Lymphocyte Activation; D010740:Phospholipases / Q000378:metabolism*; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D011493:Protein Kinase C / Q000502:physiology; D011971:Receptors, Immunologic / Q000502:physiology*; D015398:Signal Transduction; D010738:Type C Phospholipases / Q000378:metabolism*
D000945:Antigens, Differentiation, T-Lymphocyte; D001095:Arachidonic Acids; D018801:CD2 Antigens; D003512:Cyclohexanones; D011971:Receptors, Immunologic; D016718:Arachidonic Acid; C036535:1,6-bis(cyclohexyloximinocarbonyl)hexane; D000242:Cyclic AMP; D011493:Protein Kinase C; D010740:Phospholipases; D010741:Phospholipases A; D008071:Lipoprotein Lipase; D054467:Phospholipases A2; D010738:Type C Phospholipases; D002118:Calcium