title: Inhibition of activation of human T lymphocytes by the complement C1 esterase inhibitor.
abstract: The major histocompatibility complex (MHC) class I molecules have been shown to be substrates to both of the complement C1 esterases. The effect of a C1 esterase-mediated cleavage of the MHC class I molecules on the activation process of lymphocytes was investigated by including the complement C1 esterase inhibitor (C1-Inh) in the medium during activation of human peripheral lymphocytes by staphylococcal enterotoxin A (SEA). The C1-Inh was shown to inhibit the activation of both CD4+ and CD8+ cells. No effect on activation of B lymphocytes was recorded, although the complement C1 complex was shown to bind to the B lymphocytes. Furthermore, the C1 complex bound to mononuclear cells was shown to be cleaved into molecular weights corresponding to the activated forms of the C1 esterases. The effect of the C1-Inh was much more pronounced at low cell density and the inhibition was not affected by the addition of interleukin-2 (IL-2). However, the inhibition was reduced when the cells were disturbed by addition of new portions of C1-Inh, 24 and 48 hr after the initiation of the activation. This indicates that the C1-Inh interference with the activation of T lymphocytes is mediated through a mechanism that requires some form of cell contact.
mesh_terms: D003172:Complement C1 / Q000276:immunology; D003174:Complement C1 Inactivator Proteins / Q000494:pharmacology*; D004591:Electrophoresis, Polyacrylamide Gel; D004768:Enterotoxins / Q000276:immunology; D006801:Humans; D007376:Interleukin-2 / Q000276:immunology; D008213:Lymphocyte Activation / Q000187:drug effects / Q000276:immunology*; D013211:Staphylococcus aureus / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology*
chemical_list: D003172:Complement C1; D003174:Complement C1 Inactivator Proteins; D004768:Enterotoxins; D007376:Interleukin-2; C026066:enterotoxin A, Staphylococcal