Autocrine signalling

Autocrine signaling is a form of signalling in which a cell secretes a hormone, or chemical messenger (called the autocrine agent) that binds to autocrine receptors on the same cell type, leading to changes in the cells. This can be contrasted with paracrine signaling, intracrine signalling, or classical endocrine signaling.

Examples
An example of an autocrine agent is the cytokine interleukin-1 in monocytes. When this is produced in response to external stimuli, it can bind to cell-surface receptors on the same cell that produced it.

Another example occurs in activated T cell lymphocytes, i.e. when a T cell is induced to mature by binding to a peptide:MHC complex on a professional antigen presenting cell and by the B7:CD28 costimulatory signal. Upon activation, "low affinity" IL-2 receptors are replaced by "high affinity" IL-2 receptors consisting of α, β, and γ chains. The cell then releases IL-2 which binds to its own new IL-2 receptors, causing self-stimulation and ultimately a monoclonal population of T cells. These T cells can then go on to perform effector functions such as macrophage activation, B cell activation, and cell-mediated cytoxicity.