Effect of fetal thymectomy on IgG, IgM, and IgA concentrations in sheep.

Serum concentrations of immunoglobulins (Ig) IgG, IgG, IgM, and IgA were compared for normal and thymectomized lambs. Fetal thymectomies were performed in utero from 55 to 67 days of gestation. High serum IgG, IgM, and IgA concentrations occurred in all lambs after they ingested colostrum; however, the concentration of these Ig, as measured by single radial immunodiffusion, decreased exponentially during the first 16 days after birth. The half-life values for IgG, IgM, and IgA during this period in both normal and thymectomized lambs were about 25, 6, and 2 days, respectively. Increasing amounts of IgG were not detected in the serums of either group until 1 month of age. At 64 to 128 days, significantly smaller quantities of IgG and IgG were found in thymectomized lambs, whereas concentrations of IgA and IgM were similar in both groups. The results indicate that the thymus may regulate production of IgG in sheep.