We studied a case of systemic lupus erythematosus with massive pleural effusion accompanying neutrophil predominant infiltration. The presence of immune complexes and the low complement level in the effusion suggested an activation of the complement system in the pleural cavity. The effusion contained strong neutrophil chemotactic activity in the morphological polarization assay and the Boyden's chamber. From the molecular size and heat stability of the chemotactic activity, the neutrophil chemotactic factors were suggested to be C5a and the related moleules. The effusion also contained trypsin-like amidase activities against chromogenic peptide substrates. One of them was identified to be plasmin.
These results suggested that the marked effusion of the lupus pleuritis might be resulted from the neutrophil dependent vascular permeability enhancement mechanism with participation of the complement system and probably other plasma cascades.
