Kinetics of recovery of serum Ig levels and of cytoplasmic Ig positive cells in various lymphoid organs of nude mice after thymus transplantation.

The long-term effects of thymus transplantation in nude mice were studied with regard to the number of cytoplasmic immunoglobulin positive plasmablasts and plasma cells (C-Ig cells) in various lymphoid organ and their immunoglobulin (Ig) class distribution profile. These data were correlated with the serum Ig levels of the same mice. Four weeks after thymus transplantation, the number of C-Ig cells in the spleen of nude mice had increased two- to three-fold over that found in normal nude mice and normal heterozygous littermates of the same age. This overshoot subsided at 8 weeks after thymus transplantation. The increase of the C-Ig cell number in the other lymphoid organs tested (bone marrow, mesenteric lymph nodes and Peyer's patches) started later than in spleen, and did not show a clear overshoot. Almost complete recovery of the C-Ig cell pattern to that of normal littermates was found 32 weeks post-transplantation. Analysis of the Ig class distribution of the C-Ig cells showed that the increase of the C-Ig cell numbers after thymus transplantation in nude mice was almost exclusively confined to IgG1, IgG2 and IgA. The increase of C-IgG1 and C-IgG2 cells in spleen and bone marrow correlated with a simultaneous increase of the serum IgG1 and IgG2 levels, suggesting that these organs are the major source of serum IgG in young adult mice.