CS1 up-regulates tumor formation via c-maf in vivo. (A) Human λ light chain levels in blood were assayed by ELISA to assess tumor development in mice injected with indicated cells. (B) Cell surface expression of CS1 and integrin β7 on tumors in mice injected with U266 cells (U266t1-3) was analyzed by flow cytometric analysis. Red and dotted lines represent isotype control; green line, CS1 levels on excised tumor; blue line, CS1 level after 4-day culture of excised tumors. (C) Immunoblotting analysis of tumors in mice injected with indicated cells using specific Abs. (D) Hematoxylin and eosin and CD34 staining by immunohistochemistry of tumors expressing high (U266t2) and low (U266t1) levels of CS1. Images were taken using a Leica DFC300FX with a 10×/0.22 NA objective and a Leica IM50 Image Manager (original magnification, ×100).