IKK/NF-κB signaling pathways. The classical pathway is activated by a variety of inflammatory signals, resulting in coordinate expression of multiple inflammatory and innate immune genes. The alternative pathway is strictly dependent on IKKα homodimers and is activated by lymphotoxin β receptor (LTβR), B cell–activating factor belonging to the TNF family (BAFF), and CD40 ligand (CD40L). The alternative pathway plays a central role in the expression of genes involved in development and maintenance of secondary lymphoid organs. BLC, B lymphocyte chemoattractant; ELC, Epstein-Barr virus–induced molecule 1 ligand CC chemokine; MCP-1, monocyte chemoattractant protein-1; MIP-1α, macrophage inflammatory protein-1α; PLA2, phospholipase A2; SDF-1, stromal cell–derived factor-1α; SLC, secondary lymphoid tissue chemokine.