Noncanonical intercellular communication in immune response

Figure 1 Types of canonical signaling. In autocrine signaling, the cell regulates itself (autoregulates) through internally produced signaling molecules, which after release from the cell bind to cell’s own receptors. The examples are: Interleukin-1 produced by monocyte in response to external stimuli binds to its own receptor on the same monocyte; IL-2 released from activated T cell binds to its own receptor leading to self-stimulation. The juxtacrine signaling occurs between closely apposing cells when signaling molecule attached to one cell interacts with its receptor on adjacent cells or when signaling molecule excreted to the intercellular matrix of one cell binds to the receptor on neighboring cell. In juxtacrine signaling the signaling molecules do not diffuse freely between cells. The examples include cytokine signaling in immune system and Notch pathway signaling. In paracrine signaling, released signaling molecules such as, for example, cytokines or retinoic acid diffuse at short distances and act on the cells located in vicinity. In endocrine signaling, signaling molecules such as hormones or cytokines are transported through the circulation to the target cells.