Figure 1.

Intercellular molecules such as cytokines and their surface receptors can be targeted by biologics such as monoclonal antibodies, receptor-antibody fusion proteins, and, in some cases, small molecules. Intracellular enzymatic cascades convey the information from the cell surface to regulate the cell response, including transcriptional activity in the nucleus. Cell-permeable molecular compounds can block a specific kinase and transcription factors. Some surface receptors such as G-protein-coupled receptors represent another class of molecule that can be inhibited by small-molecule compounds. AP-1, activation protein-1; BLyS, B-lymphocyte stimulator; ICOS, inducible costimulator; IL, interleukin; IRF, interferon regulatory factor; LTβ-R, lymphotoxin beta receptor; NF-κB, nuclear factor-kappa-B.