Abstract
Egg yolk antibody (immunoglobulin Y, IgY), due to its unique features (e.g., cost-effectiveness for mass production), is emerging as a promising passive immune agent and alternative to antibiotics to combat infectious diseases, particularly in livestock. Oral administration of egg yolk IgY is the most common and convenient route that has been extensively investigated for controlling enteric pathogens. However, the in vivo stability of egg yolk IgY in the gastrointestinal (GI) tract, a critical issue for the success of this approach, still has not been clearly elucidated. Our recent study showed instability of orally administered egg yolk IgY in chicken GI tract, as demonstrated by both in vivo and ex vivo evidence. To better understand the magnitude and dynamics of instability of egg yolk IgY in vivo, in this study, we conducted comprehensive ex vivo analyses by spiking hyperimmune egg yolk IgY in fresh GI contents collected from five broilers at each sampling age (2, 4, or 6 weeks). The pH in gizzard slightly increased with age from 2.4 to 3.0, while the pH in the small intestine was around 5.8. ELISA analysis indicated that a short time of treatment (30 or 60 min) of IgY with the gizzard contents from the chickens at 2, 4, and 6 weeks of age greatly reduced specific IgY titer by over 8, 6, and 5 log2 units, respectively, when compared with saline control. However, small intestine content only had a mild effect on egg yolk IgY, leading to 1 log2 unit of reduction in IgY titer upon 30 min of treatment. Consistent with these findings, SDS-PAGE and immunoblotting analyses provided direct evidence demonstrating that egg yolk IgY could be drastically degraded to undetectable level in gizzard content upon as short as 5 min of treatment; however, the IgY was only slightly degraded in small intestine content. Immunoblotting also showed that treatment of IgY with HCl (pH 3.0) for 60 min did not affect its integrity at all, further supporting the enzymatic degradation of IgY in gizzard. Collectively, egg yolk IgY could be substantially degraded in chicken gizzard, highly warranting the development of effective approaches, such as encapsulation, for the controlled release and protection of orally administered egg yolk IgY in livestock.
Highlights
Chicken immunoglobulin Y (IgY) is the functional equivalent of IgG in mammals and can be transferred from serum to yolk during egg formation
As expected, the small intestine had approximate pH of 5.84 at 6 weeks of age; the pH barely changed in the corresponding supernatant used for ex vivo assay upon slight dilution with saline (Table 1)
After an additional 30 min of treatment, the specific IgY titers at the three time points were further lowered by an average of 0.5 log2 unit (Figure 1B)
Summary
Chicken immunoglobulin Y (IgY) is the functional equivalent of IgG in mammals and can be transferred from serum to yolk during egg formation. Egg yolk contains a large quantity of IgY that can confer passive immunity for chicks against pathogens, either at embryonic or post-hatching stage [1]. Immunization of hens with a particular antigen could yield a large amount of specific egg yolk IgY that has potential applications in human and veterinary medicine [2]. As an emerging alternative to antibiotics, egg yolk IgY has drawn considerable research interest in recent decades due to several unique features [2]. A laying hen is regarded as a cost-efficient “bioreactor” that can produce over 22.5 g of egg yolk IgY yearly with 2%–10% being antigen-specific [3]. Egg yolk IgY is quite stable in a wide pH range (3.5–11) and under high temperatures (up to 70°C), making it feasible for storage and processing as a feed supplement [2]
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