The morphology of mBMMC grown in the presence or absence of TGF-β₁ is compared. Cytosmears are shown from mBMMC cultured in rmIL-9/WEHI/rrSCF stained with Leishman’s stain (a) or MoAb RF 6.1 for mMCP-1 (b) and from mBMMC cultured in rhTGF-β1/rmIL-9/WEHI/rrSCF stained with Leishman’s stain (c) or MoAb RF 6.1 for mMCP-1 (d). mBMMC cultured in the presence of TGF-β1 are more rounded, lack pseudopodia, and are highly positive for mMCP-1 compared with those cultured in IL-9 alone (original magnification ×800). The ultrastructure of granules from mBMMC cultured in the presence of TGF-β₁ or in WEHI/rrSCF/rmIL-9 alone are shown in (e) and (f) (original magnification ×2,500). The granules of mBMMC supplemented TGF-β₁ mBMMC are more electron-dense.