Cell adhesion molecules (CAMs) are a subset of cell surface proteins that are involved in the binding of cells with other cells or with the extracellular matrix (ECM), in a process called cell adhesion. In essence, CAMs help cells stick to each other and to their surroundings. CAMs are crucial components in maintaining tissue structure and function. In fully developed animals, these molecules play an integral role in generating force and movement and consequently ensuring that organs are able to execute their functions normally. In addition to serving as "molecular glue", CAMs play important roles in the cellular mechanisms of growth, contact inhibition, and apoptosis. Aberrant expression of CAMs may result in a wide range of pathologies, ranging from frostbite to cancer.
Neural cell adhesion molecule (NCAM), also called CD56, is a homophilic binding glycoprotein expressed on the surface of neurons, glia and skeletal muscle. Although CD56 is often considered a marker of neural lineage commitment due to its discovery site, CD56 expression is also found in, among others, the hematopoietic system. Here, the expression of CD56 is mostly associated with, but not limited to, natural killer cells. CD56 has been detected on other lymphoid cells, including gamma delta (γδ) Τ cells and activated CD8+ T cells, as well as on dendritic cells. NCAM has been implicated as having a role in cell–cell adhesion, neurite outgrowth, synaptic plasticity, and learning and memory.
Platelet endothelial cell adhesion molecule (PECAM-1) also known as cluster of differentiation 31 (CD31) is a protein that in humans is encoded by the PECAM1 gene found on chromosome17q23.3. PECAM-1 plays a key role in removing aged neutrophils from the body.
The immunoglobulin superfamily (IgSF) is a large protein superfamily of cell surface and soluble proteins that are involved in the recognition, binding, or adhesion processes of cells. Molecules are categorized as members of this superfamily based on shared structural features with immunoglobulins ; they all possess a domain known as an immunoglobulin domain or fold. Members of the IgSF include cell surface antigen receptors, co-receptors and co-stimulatory molecules of the immune system, molecules involved in antigen presentation to lymphocytes, cell adhesion molecules, certain cytokine receptors and intracellular muscle proteins. They are commonly associated with roles in the immune system. Otherwise, the sperm-specific protein IZUMO1, a member of the immunoglobulin superfamily, has also been identified as the only sperm membrane protein essential for sperm-egg fusion.
Myelin-associated glycoprotein is a type 1 transmembrane protein glycoprotein localized in periaxonal Schwann cell and oligodendrocyte membranes, where it plays a role in glial-axonal interactions. MAG is a member of the SIGLEC family of proteins and is a functional ligand of the NOGO-66 receptor, NgR. MAG is believed to be involved in myelination during nerve regeneration in the PNS and is vital for the long-term survival of the myelinated axons following myelinogenesis. In the CNS MAG is one of three main myelin-associated inhibitors of axonal regeneration after injury, making it an important protein for future research on neurogenesis in the CNS.
Siglecs(Sialic acid-binding immunoglobulin-type lectins) are cell surface proteins that bind sialic acid. They are found primarily on the surface of immune cells and are a subset of the I-type lectins. There are 14 different mammalian Siglecs, providing an array of different functions based on cell surface receptor-ligand interactions.
CD22, or cluster of differentiation-22, is a molecule belonging to the SIGLEC family of lectins. It is found on the surface of mature B cells and to a lesser extent on some immature B cells. Generally speaking, CD22 is a regulatory molecule that prevents the overactivation of the immune system and the development of autoimmune diseases.
CD33 or Siglec-3 is a transmembrane receptor expressed on cells of myeloid lineage. It is usually considered myeloid-specific, but it can also be found on some lymphoid cells.
Signal regulatory protein α (SIRPα) is a regulatory membrane glycoprotein from SIRP family expressed mainly by myeloid cells and also by stem cells or neurons.
Sialic acid-binding Ig-like lectin 7 is a protein that in humans is encoded by the SIGLEC7 gene. SIGLEC7 has also been designated as CD328.
Sialic acid-binding Ig-like lectin 12, or Siglec-XII, is a protein that in humans, is encoded by the SIGLEC12 gene.
Sialic acid-binding Ig-like lectin 5 is a protein that in humans is encoded by the SIGLEC5 gene. SIGLEC5 has also been designated CD170.
Sialic acid-binding Ig-like lectin 9 is a protein that in humans is encoded by the SIGLEC9 gene.
Sialic acid-binding Ig-like lectin 8 is a protein that in humans is encoded by the SIGLEC8 gene. This gene is located on chromosome 19q13.4, about 330 kb downstream of the SIGLEC9 gene. Within the siglec family of transmembrane proteins, Siglec-8 belongs to the CD33-related siglec subfamily, a subfamily that has undergone rapid evolution.
Sialic acid-binding Ig-like lectin 10 is a protein that in humans is encoded by the SIGLEC10 gene. Siglec-G is often referred to as the murine paralog of human Siglec-10
The following outline is provided as an overview of and topical guide to immunology:
CD96 or Tactile is a protein that in humans is encoded by the CD96 gene. CD96 is a receptor protein which is expressed on T cells and NK cells and shares sequence similarity with CD226. The protein encoded by this gene belongs to the immunoglobulin superfamily. It is a type I membrane protein. The protein may play a role in the adhesion of activated T and NK cells to their target cells during the late phase of the immune response. It may also function in antigen presentation. Alternative splicing occurs at this locus and two transcript variants encoding distinct isoforms have been identified. CD96 is a transmembrane glycoprotein that has three extracellular immunoglobulin-like domains and is expressed by all resting human and mouse NK cells. CD96 main ligand is CD155. CD 96 has approximately 20% homology with CD226 and competed for binding to CD155 with CD226.
IgSF CAMs are cell adhesion molecules that belong to Immunoglobulin superfamily. It is regarded as the most diverse superfamily of CAMs. This family is characterized by their extracellular domains containing Ig-like domains. The Ig domains are then followed by Fibronectin type III domain repeats and IgSFs are anchored to the membrane by a GPI moiety. This family is involved in both homophilic or heterophilic binding and has the ability to bind integrins or different IgSF CAMs.
Paired receptors are pairs or clusters of receptor proteins that bind to extracellular ligands but have opposing activating and inhibitory signaling effects. Traditionally, paired receptors are defined as homologous pairs with similar extracellular domains and different cytoplasmic regions, whose genes are located together in the genome as part of the same gene cluster and which evolved through gene duplication. Homologous paired receptors often, but not always, have a shared ligand in common. More broadly, pairs of receptors have been identified that exhibit paired functional behavior - responding to a shared ligand with opposing intracellular signals - but are not closely homologous or co-located in the genome. Paired receptors are highly expressed in the cells of the immune system, especially natural killer (NK) and myeloid cells, and are involved in immune regulation.
Sialic acid-binding Ig-like lectin 6 is a protein that in humans is encoded by the SIGLEC6 gene. The gene was originally named CD33L (CD33-like) due to similarities between these genes but later became known as OB-BP1 due to its ability to bind to this factor and, finally, SIGLEC6 as the sixth member of the SIGLEC family of receptors to be identified. The protein has also been given the CD designation CD327.
