Background: Cluster of Differentiation 3 (CD3) is a multiunit protein complex expressed on the surface of T-cells that directly associates with the T-cell receptor (TCR). CD3 is composed of four polypeptides: ζ, γ, ε and δ. Engagement of TCR complex with antigens presented in Major Histocompatibility Complexes (MHC) induces tyrosine phosphorylation in the immunoreceptor tyrosine-based activation motif (ITAM) of CD3 proteins. CD3 phosphorylation is required for downstream signaling through ZAP-70 and p85 subunit of PI-3 kinase, leading to T cell activation, proliferation, and effector functions (1). Cluster of Differentiation 8 (CD8) is a transmembrane glycoprotein expressed primarily on cytotoxic T cells, but has also been described on a subset of dendritic cells in mice (2,3). On T cells, CD8 is a co-receptor for the TCR, and these two distinct structures are required to recognize antigen bound to MHC Class I (2). Cluster of Differentiation 4 (CD4) is expressed on the surface of T helper cells, regulatory T cells, monocytes, macrophages, and dendritic cells, and plays an important role in the development and activation of T cells. On T cells, CD4 is the co-receptor for the TCR, and these two distinct structures recognize antigen bound to MHC Class II. CD8 and CD4 co-receptors ensure specificity of the TCR–antigen interaction, prolong the contact between the T cell and the antigen presenting cell, and recruit the tyrosine kinase Lck, which is essential for T cell activation (2). Granzyme B is a serine protease expressed by CD8+ cytotoxic T lymphocytes and natural killer (NK) cells and is a key component of the immune response to pathogens and transformed cancer cells (4). Forkhead box P3 (FoxP3) is crucial for the development of T cells with immunosuppressive regulatory properties and is a well-established marker for T regulatory cells (Tregs) (5). CD19 is a co-receptor expressed on B cells that amplifies the signaling cascade initiated by the B cell receptor (BCR) to induce activation. It is a biomarker of B lymphocyte development, lymphoma diagnosis, and can be utilized as a target for leukemia immunotherapies (6,7). F4/80 (EMR1) is a heavily glycosylated G-protein-coupled receptor and is a well-established marker for mouse macrophages (8). CD11c (integrin αX, ITGAX) is a transmembrane glycoprotein highly expressed by dendritic cells, and has also been observed on activated NK cells, subsets of B and T cells, monocytes, granulocytes, and some B cell malignancies including hairy cell leukemia (9,10).
Background: The tumor necrosis factor receptor family, which includes TNF-RI, TNF-R2, Fas, DR3, DR4, DR5, and DR6, plays an important role in the regulation of apoptosis in various physiological systems (1,2). The receptors are activated by a family of cytokines that include TNF, FasL, TWEAK, and TRAIL. They are characterized by a highly conserved extracellular region containing cysteine-rich repeats and a conserved intracellular region of about 80 amino acids termed the death domain (DD). The DD is important for transducing the death signal by recruiting other DD containing adaptor proteins (FADD, TRADD, RIP) to the death-inducing signaling complex (DISC) resulting in activation of caspases. The two receptors for TNF-α, TNF-R1 (55 kDa) and TNF-R2 (75 kDa) can mediate distinct cellular responses (3,4). In most cases cytotoxicity elicited by TNF has been reported to act through TNF-R1 (5,6). DR3/WSL-1/Apo-3/TRAMP/LARD is a TNFR family member containing the characteristic extracellular cysteine-repeats, transmembrane region, and an intracellular DD (7-11). DR3 is activated by its ligand Apo-3L/TWEAK to induce apoptosis and activation of NF-κB (12,13). Like TNF-R1, DR3 binds to the DD adaptor protein TRADD, which can then associate with other DD proteins like FADD and RIP as well as members of the TRAF family (7,8). Tissue expression of DR3 is very restricted, primarily seen on the surface of activated thymocytes and lymphocytes and plays an important role in thymocyte negative selection (7,8,14). Studies have also indicated an association with DR3 and rheumatoid arthritis (15,16). DR4 (TRAIL-RI, TNFRSF10A) and DR5 (TRAIL-R2, TNFRSF10B) are receptors for the cytokine TRAIL. Both receptors contain death domains that recruit DISC complexes triggering caspase activation and apoptosis (17-20). DR6, also known as TNFRSF21, is a TNFR family member able to induce apoptosis as well as activation of NF-κB and JNK (21). DR6 appears to play a critical role in the activation and differentiation of T and B lymphocytes (22,23). In the nervous system, β-amyloid precursor protein (APP) activates DR6 to trigger neuronal degeneration (24).
Background: Senescence is characterized by stable stress-induced proliferative arrest and resistance to mitogenic stimuli, as well as the secretion of proteins such as cytokines, growth factors and proteases. These secreted proteins comprise the senescence-associated secretory phenotype (SASP). Senescent cells are thought to accumulate as an organism ages, and contribute to age-related diseases, including cancer, through promotion of inflammation and disruption of normal cellular function (1,2). The composition of the SASP varies, and SASP components can be either beneficial or deleterious in human disease, depending on the context (3).Senescence Associated Secretory Phenotype (SASP) Antibody Sampler Kit provides a collection of antibodies to various SASP components, including TNF-alpha, interleukin-6 (IL-6), the multifunctional cytokine IL-1beta, the chemokines CXCL10, RANTES/CCL5 and MCP-1, the matrix metalloprotease MMP3, and the serine-protease inhibitor PAI-1.
Background: Senescence is characterized by stable stress-induced proliferative arrest and resistance to mitogenic stimuli, as well as the secretion of proteins such as cytokines, growth factors and proteases. These secreted proteins comprise the senescence-associated secretory phenotype (SASP). Senescent cells are thought to accumulate as an organism ages, and contribute to age-related diseases, including cancer, through promotion of inflammation and disruption of normal cellular function (1,2).Because there is no single biomarker that can be used to definitively identify senescent cells, researchers must rely on a collection of biomarkers commonly associated with senescence. The Senescence Marker Antibody Sampler Kit provides a collection of antibodies to commonly used biomarkers of senescence-associated cell cycle arrest (p16 INK4A, p21 Waf1/Cip1), senescence-associated DNA damage (gamma-Histone H2A.X), and the SASP (HMGB1, IL-6, TNF-alpha, MMP3). The kit also includes an antibody to Lamin B1, which is frequently reduced in senescent cells.
Background: TRAFs (TNF receptor-associated factors) are a family of multifunctional adaptor proteins that bind to surface receptors and recruit additional proteins to form multiprotein signaling complexes capable of promoting cellular responses (1-3). Members of the TRAF family share a common carboxy-terminal "TRAF domain", which mediates interactions with associated proteins; many also contain amino-terminal Zinc/RING finger motifs. The first TRAFs identified, TRAF1 and TRAF2, were found by virtue of their interactions with the cytoplasmic domain of TNF-receptor 2 (TNFRII) (4). The six known TRAFs (TRAF1-6) act as adaptor proteins for a wide range of cell surface receptors and participate in the regulation of cell survival, proliferation, differentiation, and stress responses.
Background: Members of the Toll-like receptor (TLR) family, named for the closely related Toll receptor in Drosophila, play a pivotal role in innate immune responses (1-4). TLRs recognize conserved motifs found in various pathogens and mediate defense responses (5-7). TLR1, TLR2, TLR4, TLR5, TLR6, and TLR11 are localized to the plasma membrane, while TLR3, TLR7, TLR8, and TLR9 are localized to intracellular membranes including endosomal membranes. Triggering of the TLR pathway leads to the activation of NF-κB and subsequent regulation of immune and inflammatory genes (4). The TLRs and members of the IL-1 receptor family share a conserved stretch of approximately 200 amino acids known as the Toll/Interleukin-1 receptor (TIR) domain (1). Upon activation, TLRs associate with a number of cytoplasmic adaptor proteins containing TIR domains, including myeloid differentiation factor 88 (MyD88), MyD88-adaptor-like/TIR-associated protein (MAL/TIRAP), Toll-receptor-associated activator of interferon (TRIF), and Toll-receptor-associated molecule (TRAM) (8-10). This association leads to the recruitment and activation of IRAK1 and IRAK4, which form a complex with TRAF6 to activate TAK1 and IKK (8,11-14). Activation of IKK leads to the degradation of IκB, which normally maintains NF-κB in an inactive state by sequestering it in the cytoplasm. TLR1 and TLR6 associate with TLR2 to cooperatively mediate response to bacterial lipoproteins and fungal zymosan (6,15). TLR3 is an endosomal TLR that recognizes double-stranded RNA derived from viruses (7). TLR7 and TLR8 recognize single-stranded viral RNA and are also activated by synthetic imidazoquinoline compounds including R-848 (16,17). TLR9 recognizes unmethylated CpG motifs present on bacterial DNA (18).
Background: The innate immune system responds rapidly to pathogens by detecting conserved pathogen-associated molecular patterns (PAMPs) and damage/danger-associated molecular patterns (DAMPs) through pattern recognition receptors (PRRs). There are several families of PRRs. Toll-like receptors (TLRs) are transmembrane PRRs and signal through recruitment of adaptor proteins, including MyD88, which leads to recruitment and phosphorylation of IRAK1 and IRAK4, followed by activation of NF-κB and MAP kinases (1-3). Some TLRs also activate IRFs, which upregulate the type I interferon response. Activation of TLR3 and TLR4 results in phosphorylation and activation of IRF-3, while TLR7, TLR8, and TLR9 lead to activation of IRF-7 (2, 3). STING is a multi-pass ER transmembrane protein that is activated in response to intracellular DNA downstream of DNA-sensing cytoplasmic PRRs, such as DDX41, or by binding the second messenger cyclic-GMP-AMP (cGAMP) produced by cGAS (4-6). Following activation, STING translocates with TBK1 to perinuclear endosomes, leading to phosphorylation and activation of IRF-3 and NF-κB (7, 8). Following activation and translocation, STING gets phosphorylated by ULK1, resulting in STING inactivation and degradation (9). Inflammasomes are cytoplasmic multimeric protein complexes that assemble in response to PAMPs or DAMPs detected by AIM2 or members of the nod-like receptor (NLR) family, such as NLRP3 (10). Inflammasomes activate Caspase-1, which cleaves the IL-1β and IL-18 precursor proteins into the mature forms (10).