HC4073 is the recombinant form of Cobra venom factor (CVF). The complement system is the first line of defenseagainst pathogens and important component of innate as well as adaptive immunity. CVF is the non-toxic complementactivating protein in the venom from the cobra species Naja Kaouthia. CVF is a structural and functional analog ofcomplement C3. The protein functionally resembles C3b and exhibits a three-chain structure like C3c. CVF forms aC3/C5 convertase with factor B in the presence of factor D and Mg2+, thereby activating the alternative pathway ofcomplement. Although analog in function, there are two differences between CVF,Bb convertases and natural C3b,Bbconvertases. First the stability is quite different. Whereas C3b,Bb is short-lived with a half-life of 1.5 min, CVF,Bb israther stable with a half-life of 7h. Secondly, factor H disassembles C3b,Bb and serves as cofactor for proteolyticinactivation of C3b by factor I. The CVF convertase is completely resistant to factor H and I. Which makes it an excellent research tool. CVF is widely used reagent in order to deplete serum samples in order to study the role of complement in host defense, immune response and pathogenesis of disease. Since the Naja species are on the list of endangered species, native CVF will increasingly difficult to obtain. The recombinant protein (rCVF)is synthesized in insect cells and is processed into a two-chain form of pro-CSF that structurally resembles C3 (Vogel et al). Pro-CVF can present in three forms and have all functional activity of mature, native CVF. The activity of pro-CVF and the resulting convertase isindistinguishable from CVF and the C3b,Bb convertase. rCVF can be exploited in vitro as well as in animals. This leadsto decomplemented serum and high concentration of complement end products, like C3a, C5a and sTCC.