CD200 and B-cell chronic lymphocytic leukemia: In follow-up studies designed to explore the importance of sCD200 in CLL plasma in contributing to the engraftment of CLL cells in vivo, animals receiving CLL splenocytes and sCD200hi serum also received a Fab anti-CD200 mAb (1B9), while other independent groups of mice received CLL splenocytes and CLL plasma that had been depleted of CD200 by passage through an anti-CD200 CNBr column.