Mutation of the box2 domain of CRLF2 partially block signaling. (A) Triple alanine mutations were introduced across the CRLF2 box2 domain. (B) Ba/F3 cells expressing the indicated alleles were grown in TSLP beginning day 0 and cells were counted every other day. Inset shows immunoblotting for the indicated proteins. (C-D) Identical to panel B except cells were grown in the absence of cytokines.