Abstract
Immune complexes induced the synthesis of apoprotein III, the protein component of tissue thromboplastin (tissue factor) in human monocytes cultured in vitro. The response was maximal (11.1 .+-. 1.7-fold increase (mean .+-. SEM [standard error of mean]) when immune complexes were found at antigen/antibody equivalence. Immune complexes formed with the antigen-binding fragments (F(ab'')2) of Ig induced a 4.7 .+-. 1.4-fold activity increase, suggesting that another signal mechanism in addition to the Fc-receptor may be involved.