Successive immunoglobulin and cytokine expression in the small intestine of juvenile chicken.

The intestinal mucosa is of major importance for immune development. To further study the ontogeny of avian mucosal immunity, mRNA levels of IgM, IgY and IgA, the polymeric immunoglobulin receptor (pIgR) and a number of cytokines were determined at different ages in jejunum and ileum of non-immunized healthy juvenile layer chickens. Immunoglobulin genes were successively expressed in jejunum and ileum. IgM expression was maximal in week 1, IgY expression peaked in week 5, and IgA expression was most dominant after week 7 post hatch. PIgR gene expression was relatively low in the first 2 weeks post hatch, but increased thereafter. Generally, increased expression levels of IL-1, IL-10, IL-12p40, iNOS and interferon-γ mRNA levels were found between days 14-42 as compared to days 3 and 49-70 post hatch (p<0.05). Correlation was found between IgA and IL-10, TGF-β and IFN-γ expression levels on days 21, 28 and 35. Cytokine mRNA expression levels decreased to basal levels between 49 and 70 days post hatch, whereas IgA reached its maximum levels in this period. Based on the current results, we hypothesize that chicken sIgA, as mammalian sIgA, may contribute to the maintenance of intestinal homeostasis.