Application of protein arrays to apoptotic signaling pathways.Jurkat cells were treated with Fas ligand to induce apoptosis. Arrays were printed using cell lysates in serial dilutions and probed using an antibody specific to the cleaved (active) form of caspase 3. Increased cleaved caspase 3 is noted in the Fas ligand–treated cells (upper left). Hundreds of replicate arrays can be printed and probed with other antibodies; arrays then can be scanned, quantified, and compared.