Structural Biochemistry/Cell Signaling Pathways/Immune Signaling

Introduction
In immune system, the signal for cells leads to activation of different cell specific immune activities. Ligands that binds with receptors on the cell-membrane of immune systems to trigger reactions, signal transductions. Cytokines are secreted by immune cells in response to cellular signaling, and bind to specific membrane receptors, which then signal the cell via second messengers, often tyrosine kinases, to alter cellular activity (gene expression). Interleukins comprise the largest class of cytokines, and are manufactured by one leukocyte to act on other leukocytes as signaling ligands. Cytokines are often produced in cascades. Immunes signaling serves a variety of functions. There are two types of immune systems, including innate immunes system and adaptive immune system.

Different Types of Cytokine Receptors

 * Hematopoietin family receptors
 * Colony-stimulating factors (CSFs)
 * Interferon family receptors
 * Tumor Necrosis Factor family receptors
 * Chemokine family receptors

Immune Signaling in Innate Immune System
The innate immune system, known as non-specific immune system and first line of defense, defends the host from infection by other antigen in a non-specific manner. It means that the cells of the innate system recognize and respond to pathogens in a generic way. Innate immune systems provide immediate defense against infection. Pattern recognition receptors (PRR) are a class of innate immune response-expressed proteins that respond to pathogen-associated molecular patterns (PAMP) and endogenous stress signals termed danger-associated molecular patterns (DAMP). The evolutionarily more recent adaptive immune response employs diverse surface receptors that display decremental binding affinities for epitope stimuli.



Immune Signaling in Adaptive Immune System
Unlike the innate immune system, it confers long-lasting or protective immunity to the host. Antigens act as ligands for BCR, while epitope peptide•MHC complexes act as ligands for TCR. Hematopoietic growth factors stimulate cell division in immune and blood cell lines.

 Reference 

1. http://signaling-receptor.blogspot.com/2007/12/immune-signaling.html

2. Kagan, J.C, Signaling Organelles of the Innate Immune System, Volume 151, Issue 6, 7 December 2012, Pages 1168–1178