For cells, cell lines and tissues in culture till half confluency.Aplha, transcription related growth factors and stimulating factors or repressing nuclear factors are complex subunits of proteins involved in cell differentiation. Complex subunit associated factors are involved in hybridoma growth, Eosinohils, eritroid proliferation and derived from promotor binding stimulating subunits on the DNA binding complex. NFKB 105 subunit for example is a polypetide gene enhancer of genes in B cells.The receptors are ligand binding factors of type 1, 2 or 3 and protein-molecules that receive chemical-signals from outside a cell. When such chemical-signals couple or bind to a receptor, they cause some form of cellular/tissue-response, e.g. a change in the electrical-activity of a cell. In this sense, am olfactory receptor is a protein-molecule that recognizes and responds to endogenous-chemical signals, chemokinesor cytokines e.g. an acetylcholine-receptor recognizes and responds to its endogenous-ligand, acetylcholine. However, sometimes in pharmacology, the term is also used to include other proteins that are drug-targets, such as enzymes, transporters and ion-channels.