MICROVUETMiC3b EIA

The Quidel iC3b Enzyme Immunoassay measures the amount of the iC3b present in samples. Activation of either complement pathway results in the assembly of C3 convertases that cleave C3 into two fragments – C3a and C3b. The C3a fragment is one of the complement anaphylatoxins. The C3b fragment has many important biological activities, including the promotion of phagocytosis by opsonization and participation as a structural component in C3 and C5 convertases. These biological activities of C3b are under stringent control in vivo. One mechanism limiting the in vivo lifetime of C3b involves the two-site cleavage of C3b by Factor I5 with the cooperation of Factor H6 or CR17 as cofactors. Factor H is a complement control protein. CR1 is the C3b/C4b receptor found on many cell types, including red blood cells, granulocytes, monocytes, and macrophages. Factor I two-site cleavage of C3b yields inactivated C3b, called iC3b. The biological activities of C3b are lost when it is cleaved by Factor I. iC3b fragments, either in fluid phase or bound to biological surfaces, express new biological activities due to their ability to interact with CR2 and CR3 receptors on a variety of cell types. The levels of iC3b can be significantly elevated in the serum and plasma of some patients with immune complex-associated diseases such as rheumatoid arthritis and systemic lupus erythematosus. iC3b levels may also be elevated in body fluids from other patients in which complement activation is known to occur, e.g., from patients with infections, burns, myocardial infarctions, glomerulonephritis, and acute respiratory distress syndrome. The correlation between iC3b levels and the clinical status or prognosis for patients with these and other diseases remains to be determined and is a question of potential significance to the biomedical community. The Quidel iC3b Enzyme Immunoassay provides a rapid, non-radioactive, highly specific and quantitative procedure for measuring this product of C3 activation. It may also be used as a research tool to monitor the generation of iC3b in vitro.