The higher concentrations of several activation products in the pleural fluid compared with those in plasma could suggest that immune complex activation is taking place in the pleural cavity and the activation products are not leaked from the peripheral blood. Previously it has also been suggested that circulating immune complexes themselves may lead to pleural effusion by increasing capillary permeability. High concentrations of complement fragments might be due to the concentration of the complement itself or to accelerated turnover. In the present study, the ratios of complement components and their activation products were also analyzed to determine the pathway of complement activation.
Generally, rheumatoid arthritis has been considered as a disease that activates the classic pathway (high concentrations of C4d), whereas tuberculosis activates the alternative pathway of the complement system (high concentrations of Bb).> In rheumatic pleurisy, the concentrations of plasma and pleural fluid SC5b-9 have been shown to be high, and the levels of C3 and C4 in pleural fluid decreased, because of classic pathway activation. These changes were shown in our study, also. Canadian drug mall Source In rheumatic pleural fluid, the mean concentration of C4d was higher (nonsignificantly) than in tuberculous pleural fluid, and the ratio of C4d/C4 was much higher than in others, indicating activation of the classic pathway. Nevertheless, the mean concentration of factor B activation product and the ratio of Bb/factor B in rheumatic pleural fluid was as high as in tuberculous pleural effusion, reflecting the activation of the alternative pathway also. Since there was a correlation between the levels of activation products of C3 and C4, but not between the levels of activation products of C3 and factor B, this shows that activation of complement occurs more through the classic than the alternative pathway. Taken together, these findings suggest that in addition to activation of the classic pathway, some activation also occurs through the alternative pathway in rheumatic pleural fluid.