Effects of MHC class II cross-linking on the activation of PI3 kinase, p38MAPK, and p42/44ERK. Peripheral blood monocytes differentiated into immature DCs for 7 days with GM-CSF and IL-4 were stimulated with human IgG1, LAG-3Ig, or a class II–specific mAb (I3) as described in the legend to Figure 2. Cell lysates were analyzed by probing Western blots with phosphorylation-specific antibodies against the PI3 kinase substrate Akt (A), the kinase p38 MAPK (B), and p42/44 ERK (C). Blots were reprobed with antibodies specific for total antigen to verify equal loading of samples. Results are representative of 3 experiments performed on different DC samples.