TSH-producing BM cells are not associated with mature T cells, developing B cells, or Thy-1⁺ BM cells.

To further characterize the cellular source of TSH within the BM, cells were stained with anti-TCRβ chain mAb as an indicator of mature αβ T cells, with anti-B220 mAb as an indicator of developing B cells, or with anti–Thy-1 mAb because low levels of Thy-1 are expressed on a population of early BM stem cells. Note that in all cell populations (R1, R2, and R3), only a very small percentage of the total intracellular TSH⁺ cells were mature T cells, developing B cells, or stem cells, further confirming that the primary source of TSH in the BM is a population of CD11b⁺ cells.