IgY antibodies for the immunoprophylaxis and therapy of respiratory infections

Abbas, Aymn Talat; El-Kafrawy, Sherif Aly; Sohrab, Sayed Sartaj; Azhar, Esam Ibraheem Ahmed

Passive immunization is the administration of preformed antibodies or immunoglobulins to treat various infectious diseases. 24, 25, 30 Passive immunity can be either natural or acquired. 24, 31 Maternal antibodies transferred to the offspring deliver protection against pathogens, which represents natural passive immunity. In birds, the egg yolk is the reservoir of the circulating IgYs, which then enter the embryonic circulation of the developing embryo. 32, 33 The maternal IgYs provide protection for a very short time (about 2 weeks), and their levels in the chicks' blood decrease rapidly after 1 week from hatching, when the young birds begin to synthesize their own antibodies. 34 Passive immunity can also be artificially induced by transferring antibodies or serum derived from immune subjects to non-immune subjects by systemic, intravenous, or oral routes. Owing to the short-term nature of passive immunity, a continuous supply of the preformed antibodies is needed, which requires that they be produced on a large scale. 35 Such production of large quantities of IgY antibodies from egg yolk can be achieved via hyperimmunization of chickens. The process includes the immunization of hens with specific antigens at regular intervals for continuous production of IgYs in the egg yolks. Extraction of these IgYs from egg yolks ensures a constant supply of the antibodies. 36 Passive immunization was first introduced more than 100 years ago by Albert Calmette and others. 37 The passive immunization principle has since been extensively used for treating and preventing diseases in humans and animals.-31,38,39 An expected advantage of antibody-based treatments is the absence of off-target resistance or altered distribution of the host flora because the treatments target specific diseasecausing pathogens. 40 Intranasal antibody prophylaxis, which is based on the passive immunity principle, was reported to show promise against viral respiratory infections in animal models, including respiratory syncytial virus (RSV), influenza virus, and Sendai virus, and it was expected to show good efficacy in human clinical trials for influenza A and B viruses, Coxsackie virus, and rhinoviruses. However, studies showed low antiviral efficacy of the antibodies used and suggested that this result might be attributable to low levels of viral-specific antibodies in the immunoglobulin (Ig) preparations used. 41