The OD values observed during the antigen–antibody interaction of the positive reference serum with the HAH5 protein purified or directly from the culture supernatant produced in different expression systems were very similar, as well as the OD values detected

when the negative reference serum was assayed. Despite the differences in the viral vector and HSP targets the expression system used, it seems that the HAH5 protein did not suffer dramatic post-translational changes during its production and posterior secretion able to alter its recognition by antibodies. Thus, the use of the HAH5 protein directly from the culture supernatant for the recognition of anti-HAH5 antibodies could lower the costs in a large scale process because of the exclusion

of the purification stage. On the other hand, the fact that the HAH5 protein purified by IC have shown a similar antibody levels compared with the unpurified variant when the sera of chickens immunized with the HACD protein purified by IC was assayed is a very interesting result. There are evidences that the renaturation after the acidic elution during the purification by IC of the HACD protein make it inefficient to induce HIA, while the same BIBW2992 cost protein purified by SEC is able to induce such type of antibodies [8]. This suggests that HAH5 molecule purified by IC could undergo conformational Farnesyltransferase changes upon renaturation. Regardless of the failure in inducing hemagglutinating antibodies, the HACD protein purified by IC is able to trigger a humoral immune response detected by ELISA containing antibodies able to recognize both the HAH5 protein purified by IC or directly from the culture supernatant. Also, the antibodies induced by the HACD protein purified by SEC bind the HAH5 protein purified by IC. Therefore, the protein HAH5, although purified by a method that can affect its conformation, preserves epitopes able to bind antibodies induced by a protein with a conformation very close

to the native HA. It suggests there are other antibodies than HIA which are induced during the immune response against the HA protein that, although incapable of neutralizing the molecule, can be detected in ELISA assays using the HA protein purified by IC. Hence, this protein can be useful in diagnostic by detecting H5 subtype of avian influenza virus. There is no doubt that avian influenza caused by HPAIV H5N1 is one of the viral diseases which currently could put in danger poultry and all mankind with the sudden appearance of a new strain able to cross species from birds to human and rapidly propagate among them. Consequently, there are a lot of research projects directed to basic investigations for controlling and making better surveillance methods to eradicate this disease.