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IgM-forming cells as the immediate precursor of IgA-producing cells during ontogeny of the immunoglobulin-producing system of the chicken.


 Chickens bursećtomized at hatch and treated with either anti-α or anti-µ had depressed serum levels of both IgM and IgA, whereas IgY production was unaffected. Chickens bursectomized at hatch and treated with anti-α + anti-µ combined had more severely depressed levels of serum IgM and IgA than bursectomized chickens treated with either antibody alone. The suppressive effects of anti-µ on IgA, anti-α on IgM, and the the additive suppressive effect of combined antibody treatment on both IgM and IgA suggest that IgA-producing cells are derived from IgM-forming precursor cells through a doubly-producing intermediate. The lack of suppressive effect on IgY production in birds having severe depression of IgM and IgA indicates that few if any IgY-forming cells serve as precursors for IgA-producing cells.