CD4

The role of MHC Class II RT1B and immune response post brain injury

The major histocompatibility complex (MHC) is responsible for binding peptide fragments arising from pathogens in order to display them on the cell surface for recognition from immune cells.  Once recognized, the foreign pathogen is typically evaded. The MHC complex is broken into two categories, MHC Class I proteins and MHC Class II proteins.  MHC complex I and II proteins are all very different and contain specific molecules to bind different peptides – in fact, they have been described as the most polymorphic genes there are.

Topics in CD11b: The innate immune response

Integrins are transmembrane receptors composed of alpha and beta chains, where beta-integrins are mainly expressed in leukocytes. Leukocytes are white blood cells that act in the immune system to defend our body against foreign pathogens.

Transferrin and the blood brain barrier

Transferrin, an iron binding protein that facilitates iron uptake in cells, is an integral part of a mechanism that may introduce antibody therapies to the central nervous system. Currently, the brain’s ability to take in antibody therapies is limited by the presence of the blood brain barrier.

MHC Class I and the Herpes Simplex Virus

MHC molecules (also known as major histocompatibility complex molecules) assist in the presentation of antigens to T cells in order to eradicate foreign pathogens.  These molecules are highly polymorphic, meaning that they exist in multiple variants in order to avoid pathogens evading their activation of the immune response.  MHC Class I molecules in particular deliver cytosolic peptides to the cell surface so that they can continue on through the cytosol and ultimately the endoplasmic reticulum (ER).

CD3 (OKT3) as a marker of immune response efficiency

Our immune system is a powerful defense mechanism against infection, however different variables can cause our immune response to work for or against us.  CD3 (cluster of differentiation 3) is one component of our immune signal response that is composed of four distinct chains (CD3-g, CD3-e, CD3-s and the zeta chain). These chains associate with a molecule known as the T-cell receptor (TCR) to comprise the TCR complex.

CD20 (Cluster of differentiation 20, Membrane-spanning 4-domains subfamily A member 1 (MS4A1), CVID5, B-lymphocyte surface antigen B1)

CD20 is a human B-lymphocyte surface molecule that spans the membrane four times and is expressed on both normal and malignant cells. The CD20 antigen displays a unique expression pattern among hematopoietic cells - it is present on human pre B-lymphocytes and B-lymphocytes at all stages of maturation (except for plasma cells). Low CD20 antigen expression levels have been detected on normal T-lymphocytes. It functions as a B-cell activation receptor and B-lymphocyte development and differentiation agent, presumably through modulating intracellular calcium levels.

CD8 alpha - Marker for cytotoxic T lymphocytes

The T-cell co-receptor CD8 is a cell-surface glycoprotein that bridges the lipid bilayer by interacting externally with ligands, such as major histocompatibility complex (MHC) class I, as well as internally with signaling molecules such as tyrosine kinase p56 lck. CD8 associates with lck through a zinc clasp structure and down regulates major Th2-type cytokine production.

Lymphocyte activation gene 3 (LAG3): No lag time in immune response

The LAG3 protein belongs to the Ig superfamily and contains 4 extracellular Ig-like domains (D1-D4). This molecule plays an key role in the immune response through negative regulation of T-cell proliferation, function, and homeostasis. It is required for maximum natural and induced regulatory T-cell function. LAG3 is closely related to the T-cell co-receptor CD4, and like CD4, binds to MHC class II molecules - but with a significantly higher affinity. It is expressed exclusively in activated T- and natural killer (NK) lymphocytes.

CD4 - An Important Co-receptor Assisting TCRs

The cluster of differentiation 4 (CD4) protein is a surface, type I membrane-embedded glycoprotein that is found on a wide range of cells: T-lymphocytes, B-cells, macrophages, granulocytes, and developmentally-dependent regions specific to the brain. It interacts with major histocompatibility complex (MHC) class II anti-genes, serves as the human immunodeficiency virus (HIV) receptor, and can initiate/augment early phase T-cell activation.  In immune-mediated and central nervous system (CNS) infectious diseases, CD4 indirectly mediates neuronal damage.

CD4, HIV and T Cell Signaling

CD4, also known as Cluster of Differentiation 4, interacts with major histocompatibility complex class II antigens, acts as a receptor for the human immunodeficiency virus and induces the aggregation of lipid rafts. It is expressed in T lymphocytes, B cells, macrophages, granulocytes, dendritic cells and specific regions of the brain.

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