title: Leukocyte complement: a possible role for C5 in lymphocyte stimulation.
abstract: The results presented here show that Fab' antibody fragments directed to complement proteins C5, C6, and C7 inhibit lymphocyte stimulation in mixed lymphocyte culture (MLC) by up to 65%, as determined by decreased incorporation of 3H-thymidine. Lymphocyte stimulation induced by PHA-mitogen was also inhibited up to 100% by anti-C5 Fab'. Specificity of these reactions was established by the findings that goat anti-C5 or murine hybridoma anti-C5 both inhibited MLC; the inhibitory activity of anti-C5 Fab' was absorbed with highly purified C5 (but not with C3), and antibody directed to C3 did not inhibit lymphocyte stimulation by MLC or PHA. The effects of anti-C5 were exerted in a nontoxic manner. Cleavage of lymphocyte associated C5 with factor B (Bb) or with trypsin resulted in stimulation of lymphocyte thymidine incorporation. Purified C5a was found to induce lymphocyte stimulation in serum-free medium in pulse-chase types of experiments. Anti-C6 and C7 Fab' also inhibited lymphocyte stimulation induced in one-way MLC. These results suggest that C5, C5a, and/or C6 and C7 may play a role in triggering of lymphocyte blastogenesis.
mesh_terms: D000818:Animals; D003182:Complement C5 / Q000276:immunology*; D003183:Complement C6 / Q000276:immunology; D003184:Complement C7 / Q000276:immunology; D015938:Complement Membrane Attack Complex; D003165:Complement System Proteins / Q000276:immunology; D007140:Immunoglobulin Fab Fragments; D008213:Lymphocyte Activation; D007959:Lymphocyte Culture Test, Mixed; D051379:Mice
chemical_list: D003182:Complement C5; D003183:Complement C6; D003184:Complement C7; D015938:Complement Membrane Attack Complex; D007140:Immunoglobulin Fab Fragments; D003165:Complement System Proteins