Evaluation of a receptor gene responsible for maternal blood IgY transfer into egg yolks using bursectomized IgY-depleted chickens

Abstract

In avian species, maternal immunoglobulin Y (IgY) is transferred from the blood to the yolks of maturing oocytes; however, the mechanism underlying this transfer is unknown. To gain insight into the mechanisms of maternal IgY transfer into egg yolks, IgY-depleted chickens were generated by removing the bursa of Fabricius (bursectomy) during egg incubation, and their egg production and IgY transport ability into egg yolks were determined. After hatching, blood IgY concentrations of the bursectomized chickens decreased gradually until sexual maturity, whereas those of IgA remained low from an early stage of growth (from at least 2 wk of age). Chickens identified as depleted in IgY through screening of blood IgY and IgA concentrations were raised to sexual maturity. At 20 wk of age, both blood and egg yolk IgY concentrations in the IgY-depleted group were 600-fold lower than those of the control group, whereas egg production did not differ between the groups. Intravenously injected, digoxigenin-labeled IgY uptake into the egg yolk was approximately 2-fold higher in the IgY-depleted chickens than in the controls, suggesting that IgY depletion may enhance IgY uptake in maturing oocytes. DNA microarray analysis of the germinal disc, including the oocyte nucleus, revealed that the expression levels of 73 genes were upregulated more than 1.5-fold in the IgY-depleted group, although we could not identify a convincing candidate gene for the IgY receptor. In conclusion, we successfully raised IgY-depleted chickens presenting a marked reduction in egg yolk IgY. The enhanced uptake of injected IgY into the egg yolks of the IgY-depleted chickens supports the existence of a selective IgY transport mechanism in maturing oocytes and ovarian follicles in avian species.

Keywords: IgY depletion; bursectomy; chicken; egg yolk; maternal IgY transfer.

Figure 1

Time course of change in the body weight of control and IgY-depleted chickens. Bars indicate the mean ± SEM of 5 chickens. IgY, immunoglobulin Y.

Figure 2

Time course of changes in blood IgY (A) and IgA (B) concentrations of control and IgY-depleted chickens. The IgY and IgA concentrations were measured by ELISA. Bars indicate the mean ± SEM of 5 chickens. IgY, immunoglobulin Y.

Figure 3

Concentrations of blood IgY (A) and egg yolk IgY (B) in laying control and IgY-depleted chickens at 21 wk of age. Bars indicate the mean ± SEM of 5 chickens. IgY, immunoglobulin Y.

Figure 4

Egg yolk uptake of intravenously injected IgY in control and IgY-depleted chickens at 22 wk of age. DIG-labeled IgY was injected at 100 μg/bird into the wing vein. Laid eggs were collected daily until day 7 after injection, and IgY uptake into the yolks was measured by ELISA. Bars indicate the mean ± SEM of 5 chickens. Significantly different from the control at *P < 0.05, **P < 0.01. IgY, immunoglobulin Y.