(A) Photomicrographs of thymic tissues of Tg-mice injected with serum/PBS (A-1) and 500 ng of hGM-CSF (A-2) twice daily for 1 week. Note voluminous medulla on Tg-mice treated with serum/PBS as compared with a drastic involution on Tg-mice treated with hGM-CSF. (B) Dose-response effects of hGM-CSF on cell number of thymic cells in Tg-mice. (C) Flow cytometric analysis of thymic cells from normal littermates (left) and Tg-mice (right) treated with 500 ng of hGM-CSF. Thymic cells were stained with FITC-anti-CD8 and PE-anti-CD4.