Western blot analysis of the specificity of the rabbit polyclonal antibody directed against murine Mpl. The same amount of protein lysate from Ba/F3 and Ba/F3-mu-Mpl cells was analyzed, and two concentrations of the anti-Mpl antibody were used. Nonrelevant rabbit purified immunoglobulins were used as a control. The size of protein markers is indicated on the right of the figure.