Ligation of MyD-1 induces tyrosine phosphorylation and recruitment of SHP-2. Cells of the human monocyte cell line U937, which expresses surface MyD-1 (results not shown), were incubated in the presence and absence of murine anti-human MyD-1 antibody (ILA24; 10 μg/mL) for up to 60 minutes at 37°C and immune complexes prepared. The induction of tyrosine phosphorylation after crosslinking MyD-1 was assessed by Western blot analysis of anti-MyD-1 immune complexes using the anti-phosphotyrosine mAb, 4G10 (A). Similarly, anti-MyD-1 immune complexes were assessed for MyD-1 (B), SHP-1 (C), or SHP-2 (D) expression as indicated.