The most widely used measures of complement activation are the monitoring of the C3 or C4 components of the cascade. The classic pathway consumes both C3 and C4, sparing factor B, whereas the alternative pathway activation consumes C3 and factor B, sparing C4. However, the concentrations of complement components may reflect, not only the consumption, but also, the synthesis of the components. Synthesis is greater than normal in acute phase reactions, during inflammation, and infection.
However, the synthesis may be lower than normal in some diseases, for example in systemic lupus erythematosus, and the complement consumption may then be masked.
By measuring concentrations both of various components of complements and of their activation products, it is possible to decide which pathway is prevailing More info online antibiotics. High concentrations of C4 activation product (C4d) reflect classic pathway activation, and high concentrations of factor B activation product (Bb) reflect alternative pathway activation. When either the classic or the alternative pathway is activated, the concentrations of C3 activation product (C3d) and SC5b-9 are increased.
Detection of complement complexes or fragments in biological fluids directly indicates complement activation; finding SC5b-9 complexes indicates that membrane attack complexes may also have formed at sites adjacent to the fluid; and elevated C4d and Bb may reflect decay of C3 by its convertases, arising by the classic and alternative pathways, respectively.
Pleural effusion is a common complication associated with a variety of local and systemic diseases. The most common reasons for pleural effusion include malignancies, infections, tuberculosis, pulmonary embolism, congestive heart failure, and systemic autoimmune diseases. The cause of about one third of pleural effusions remains unknown, despite thorough examinations. Although there are studies that have shown complement activation in pleural fluid, especially in patients with rheumatoid arthritis and also in tuberculosis, the connections between complement activation, various components of complements, and the etiology of pleural fluid have not been thoroughly examined previously (to our knowledge).