Imgenex

Immunology is a broad branch of biomedical science that covers the study of all aspects of the immune system in all organisms. The immune system is the body's defense against infectious organisms and other invaders. Through a series of steps called the immune response, the immune system attacks organisms and substances that invade our systems and cause disease. The immune system is made up of a network of cells, tissues, and organs that work together to protect the body. The immune system is the body’s natural defence in combating organisms. The immune system usually have two lines of defence: the innate immune system representing a non-specific (no memory) response to antigen (substance to which the body regards as foreign or potentially harmful) and the adaptive immune system, which displays a high degree of memory and specificity. The innate system represents the first line of defence to an intruding pathogen and includes various cells like the natural killer (NK) cells, mast cells dendritic cells and phagocytes. Besides there are molecules like complement, acute phase proteins (APP) and interferons (IFNs) which work in concert with the cells of the innate immune system and which foster close functional links with their adaptive counterpart. The adaptive immune system is further divided into humoral and cellular components.  Cell-mediated immunity, also known as delayed-type hypersensitivity (DTH) or Type IV Hypersensitivity, is an immune response that does not involve antibodies but rather involves the activation of macrophages, natural killer cells (NK), antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen. The humoral immune response (HIR) is the aspect of immunity that is mediated by secreted antibodies, produced in the cells of the B lymphocyte lineage (B cell). When activated by foreign antigen, B cells undergo proliferation and mature into antibody secreting plasma cells which posses the ability to secrete soluble proteins (antibodies). Antibodies which are classified into five different types (known as isotypes), namely IgM, IgG, IgA, IgE and IgD, have two roles to play - the first is to bind antigen and the second is to interact with host tissues and effector systems in order to ensure removal of the antigen. Thus the immune system generally is protective, however the same immunologic mechanisms that defend the host at times may result in severe damage to tissues and, occasionally, may cause death.

Conceptualizing the natural antigen- antibody development & interaction, Imgenex Corp. develops and commercializes novel reagents for the scientific study of human biology and disease and for the production of new diagnostic assays and potential therapies of such diseases. These novel reagents include antibodies, gene and protein expression systems, and arrays of various cells and tissues for use in studies of functional genomics. Areas of biological interest at IMGENEX include cancer, apoptosis (programmed cell death), molecular signaling pathways, cellular aging, and metabolic and infectious diseases.

Early development and differentiation of nascent T cells that migrate from bone marrow to become mature, naïve T cells, which are capable of responding to antigen takes place inside the thymus. Around 10¹⁰ TCR (T cell receptor) variations are generated in developing T lymphocyte clones through a random process of somatic cell gene reorganization. During this process, often T-cells recognizing self-antigens are generated. Due to the ability of these self-reactive T-cells to elicit an autoimmune attack, they are permanently removed by the thymus through negative selection and clonal deletion. But, some of them manage to escape the thymic defenses and harbor themselves in the peripheral lymphoid organs. In periphery, T lymphocytes undergo further differentiation into effectors of various immune functions.

One of many immunotolerance mechanisms that immune system has developed to distinguish between self and non-self antigens is regulatory T cells or Tregs. These cells are recently characterized specialized T-cell subsets that actively suppress a variety of immune responses. Researchers have broadly classified Tregs into natural and adaptive Tregs. Natural Tregs are CD4⁺CD25⁺ T-cells that originate in the thymus and play a significant role in immune homeostasis and protection against autoimmunity. Adaptive Tregs are non-regulatory CD4⁺ T-cells that have up-regulated CD25 expression during pathological and inflammatory conditions such as cancers and infections.

Although the principal immunosuppressive mechanism of Tregs remains elusive, several in vivo experimental models have indicated that Tregs secrete large amounts of immunosuppressants including IL-9, IL-10 and TGF-β upon activation. These lymphokines are capable of inhibiting activation of Th1, Th2 cells and CTLs required for cell-mediated immunity, inflammation and antibody production. Certain recent experimental data and results even indicate that IL-2-IL-2R signaling is vital for development, maintenance, survival, expansion and suppressive activity of Tregs. Increased expression of certain other characteristic markers including CTLA-4, glucocorticoid-inducible tumor necrosis factor receptor (GITR) and OX40 has been identified on Tregs whose function inside these cells is still not clear. The TCRs displayed on Tregs are capable of recognizing and interacting with any peptide-MHC class II ligand having certain range of avidity. But, the contribution of TCR signaling and role of TCR-ligand interactions towards regulatory T-cell development needs to be determined.

Several elegant experiment using transgenic mice and retrovirus mediate over expression studies, researchers have identified FoxP3, a transcription factor, to be a specific molecular marker essential for the development and function of Tregs. The primary evidence regarding the involvement of FoxP3 in the development of Tregs was provided by the experiments of Sakaguchi et al, (ref ?) in patients suffering from IPEX, a rare and fatal human autoimmune disorder. In these patients, mutated FoxP3 gene causes improper development of Tregs resulting in hyperactivation of T-cells reactive to self-antigens. Recently, experiments have clearly shown that retroviral mediated introduction of FoxP3 into conventional CD4+ T-cells converts them into regulatory T-cells.

The emergence of regulatory T-cells and role of FoxP3 as a critical player in the negative control of a of various normal and pathological immune responses holds great promise for the development of novel therapies useful for the treatment of autoimmune diseases in humans. However, there are several questions that remain to be answered including the basic biology of the Tregs, various ligands responsible for thymic selection of these cells, the exact function of FoxP3 in relation with various markers present on Tregs and most importantly, the mechanisms by which Tregs exert their suppressive effects. A better understanding of manipulating FoxP3 and Tregs would enable us to harness the tremendous therapeutic potential in various clinical situations including Type I diabetes, Multiple sclerosis, GVHD, rheumatoid arthritis, allergy, and cancers.

FOXP3 is a master regulator of immune homeostasis expressed specifically in CD4⁺ CD25⁺ T regulatory cells controlling their growth, development and function.  FOXP3 significance in the normal development of Tregs is better elucidated with the fact that mutated FOXP3 results in a rare and fatal early onset autoimmune disorder in humans called XLAAD/IPEX (human immune dysregulation, polyendocrinopathy, enteropathy, X-linked syndrome), a condition phenotypically similar to Scurfy in mice. 

FOXP3is primarily an oligomeric, transcriptional repressor protein that belongs to the P subfamily of forkhead (FKH)-winged helix family of transcriptional factors. Members of this subfamily are forkhead (FKH) box proteins characterized by the presence of a highly conserved C-terminal winged-helix/FKH DNA binding domain (DBD) and centrally-located C2H2 zinc finger domain and leucine zipper domain.  Apart from these, an additional N-terminal proline rich region is present in FOXP3, whose function is yet to be understood. Studies have shown that FOXP3 is a nuclear-localized protein that specifically trans-represses NF-AT-induced expression of cytokines and other transcriptional factors in Tregs including IL-2, IL-4, IFN-gamma and NF-κB.

However, FOXP3 is not the sole master switch regulating the origin and development of CD4⁺ CD25⁺ Tregs. Studies have confirmed the existence of splice variant forms FOXP3 that are specifically expressed in humans but are lacking in mouse. Cloning and RT-PCR analysis from mRNA of CD4⁺ CD25⁺ T regulatory cells (Allan et. al, Smith et. al) has shown that these cells express two different alternatively spliced variant forms of FOXP3. While the FOXP3Δ2 variant had a deleted 105bp exon2 region, there was another FOXP3Δ2, Δ7 variant that had an additional 81bp exon7 deletion apart from exon2 deletion. The predicted molecular weight of this FOXP3Δ2 is ~4KDa lower than the molecular weight of FOXP3.  Transient transfection assays using Jurkat cells suggest that the FOXP3Δ2 is novel splice variant that functions as a transcriptional repressor protein and acts in cohort with FOXP3 causing a significant suppression of cytokines and up-regulating the expression of various Treg-associated markers.

The existence of the splice variant forms of FOXP3 protein suggests an additional level of complexity related to the biology of FOXP3.  A lot research needs to be done so as to elucidate the physiological and functional importance of FOXP3 splice variant forms towards maintaining immune homeostasis in Tregs and preventing autoimmune disorders.

ATM, the gene product mutated in the cancer susceptibility syndrome ataxia–telangiectasia, is related to proteins involved in DNA repair and cell-cycle control. It encodes a nuclear 350 kDa phosphoprotein containing a carboxy terminus phosphatidylinositol 3-kinase (Pl-3 kinase) catalytic domain shared by members of a superfamily of large eukaryotic proteins involved in intracellular signaling, DNA-damage induced cell cycle checkpoints, DNA repair and recombination. It was discovered as mutated proteins in patients with ataxia-telagiectasia (A-T), a severe genetic disorder characterized by cerebellar degeneration, neuromotor dysfunction, chromosomal instability, immune system defects, cancer predisposition, and acute sensitivity to ionizing radiations. In undamaged cells it is present as a dimer or oligomer molecule in which the kinase domain is silent because associated with the FAT region of another ATM monomer. Following DSB formation, it rapidly autophosphorylates on residue Serine 1981, and the inactive ATM dimers are converted (dissociated) into active ATM monomers. Active phosphorylated ATM molecules interact and phosphorylate downstream proteins that affect one or more of the cell cycle checkpoints. Some of the known substrates are the p53 protein and its ubiquitin ligase, MDM2; the Nbs1 protein; the Brca1 protein, which interacts with other repair proteins; the checkpoint kinase 2, Chk2; the Rad17 protein and the chromatin remodeling protein SMC1. Phylogenetic analyses reveal that the ATM protein is most closely related to several very large proteins that define a subgroup of the PI 3-kinase family which include the Schizosaccharomyces pombe Rad3 protein and its probable Saccharomyces cerevisiae homologue, Mec1p/Esr1p. Other proteins in the ATM family are S. cerevisiae Tor1p and Tor2p and their mammalian counterpart FRAP, which function, at least in part, by controlling progression through the G1 phase of the cell cycle. The ATM gene provides instructions for making a protein that is located primarily in the nucleus of cells, where it helps control the rate at which cells grow and divide and also assists cells in recognizing damaged or broken strands of DNA. It has been suggested that it acts as a lipid kinase, and feeds the phosphorylated lipids into signaling pathways to regulate cell-cycle progression or the activity of DNA-repair components. It regulates NF-κB activity and control the transcription of many genes that play important roles in the development and function of the immune system. In the DNA-damage response pathway, it acts upstream of p53 to induce cell cycle arrest at the G1/S and G2/M boundaries and a slowing of the S-phase. Signalling by ATM involves interactions with and phosphorylation of critical molecules, including the mitotic checkpoints Chk1 and Chk2. Apart from its role in ataxia telangiectasia (AT), ATM gene mutations have also been found in T-cell prolymphocytic leukaemia patients with no family history of AT and in non-Hodgkin’s lymphomas.

Coined in the 1960's,apoptosis is derived from the Greek word apopiptein which means to fall off from. Apoptosis can be induced by a number of stimuli including UV damage, irradiation, drug treatment, or tumor necrosis factor. Once induced, apoptosis can, in turn, act through a number of different cell death signaling pathways.

The number of apoptosis and 'programmed cell death' related kits and reagents available to the market have increased significantly over the last few years.  This is in large part the result of increasing evidence implicating the role of apoptosis in a number of significantly relevant disease processes including certain autoimmune diseases, transplantation rejection, and neurodegenerative diseases.  IMGENEX offers over 200 Apoptosis related antibodies, as well as ELISA kits, caspase inhibitors, active caspase detection kits, apoptosis detection kits, and   mitochondrial permeability detection kits.