antigen presenting cell

(noun)

A cell that presents captured antigens to immature T-cells. Dendritic cells and macrophages are the best examples, but several other cells can present antigens as well.

Related Terms

Examples of antigen presenting cell in the following topics:

  • Antigen-Presenting Cells

    • Antigen presentation is a process where immune cells capture antigens and then enable their recognition by T-cells.
    • Some cells, however, are specially equipped to acquire and present antigen, and prime naive T cells.
    • Antigen presentation stimulates T cells to become either "cytotoxic" CD8+ cells or "helper" CD4+ cells.
    • MHC Class I molecules present antigen to CD8+ cytotoxic T cells.
    • In the upper pathway; foreign protein or antigen (1) is taken up by an antigen-presenting cell (2).

  • Lymphocytes

    • Subtype 2 helper T cells present antigens to B cells.
    • Memory T cells are created after an adaptive immune response subsides, retaining the presented antigen.
    • During antigen presentation, antigen-presenting cells first present antigens to T cells.
    • They are specific to the antigen presented to that BCR and rapidly secrete large amounts of antigen-specific antibodies to prevent reinfection if that antigen is detected again.
    • Besides antibody production, B cells may also function in antigen presentation, though not to the degree of macrophages or dendritic cells.

  • Antigenic Determinants and Processing Pathways

    • Epitopes determine how antigen binding and antigen presentation occur.
    • The determinants need not be located on the exposed surface of the antigen in its original form, since recognition of the determinant by T cells requires that the antigen be first processed by antigen presenting cells.
    • In order for an antigen-presenting cell (APC) to present an antigen to a naive T cell, it must first be processed so itacan be recognized by the T cell receptor.
    • There, they are recognized by the T cell receptor on a T cell during antigen presentation.
    • The endogenous pathway occurs when MHC class I molecules present antigens derived from intracellular (endogenous) proteins in the cytoplasm, such as the proteins produced within virus-infected cells.

  • Specific T-Cell Roles

    • Differentiation for most categories of T cells occurs during the the T cell maturation, but memory cell and helper T subset differentiation occurs after maturation following antigen presentation.
    • Their primary functions include antigen presentation and activation of B cells, and activation of cytotoxic T cells and macrophages.
    • Helper T cells become activated when presented with peptide antigens by MHC class II molecules, which are expressed on the surface of antigen-presenting cells.
    • They recognize their targets by binding to antigens associated with MHC class I, which is present on the surface of nearly every cell of the body.
    • Unlike conventional T cells that recognize peptide antigens presented by major histocompatibility complex (MHC) molecules, NKT cells recognize glycolipid antigen presented by a molecule called CD1d.

  • Antigens and Antigen Receptors

    • Cells present their immunogenic-antigens to the immune system via a histocompatibility molecule.
    • Depending on the antigen presented and the type of the histocompatibility molecule, several types of immune cells can become activated.
    • By endocytosis or phagocytosis, exogenous antigens are taken into the antigen-presenting cells (APCs) and processed into fragments.
    • Tumor antigens or neoantigens are those antigens that are presented by MHC I or MHC II molecules on the surface of tumor cells.
    • These antigens can sometimes be presented by tumor cells and never by the normal ones.

  • Overview of Adaptive Immunity

    • The recognition of specific "non-self" antigens in the presence of "self" during the process of antigen presentation
    • The antigen for the pathogen is taken up by an antigen-presenting cell (APC), such as a dendritic cell or macrophage, through phagocytosis.
    • The antigen is presented to immature helper T cells and cytotoxic T cells through binding the MHC II (helper T) or MHC I (cytotoxic T) to T-cell receptors.
    • Helper T cells activate B cells, which proliferate and produce antibodies specific to the antigen, while cytotoxic T cells destroy pathogens that bear the antigen that was presented to them by the APCs.
    • Antigen presentation stimulates T cells to become either "cytotoxic" CD8+ cells or "helper" CD4+ cells.

  • Maturation of B Cells

    • The principal functions of B cells are to make antibodies against antigens, perform the role of antigen-presenting cells (APCs), and eventually develop into memory B cells after activation by antigen interaction.
    • When the B cell receptor, on the surface of the cell matches the detected antigens present in the body, the B cell proliferates and secretes a free form of those receptors (antibodies) with identical binding sites as the ones on the original cell surface.
    • After activation, the cell proliferates and B memory cells would form to recognize the same antigen.
    • Other functions for B cells include antigen presentation, cytokine production, and lymphoid tissue organization.
    • B cells that encounter antigen for the first time are known as naive B cells.

  • Clonal Selection and T-Cell Differentiation

    • T and B cells are able to respond to nearly all of the world's vast variety of antigens upon presentation.
    • During antigen presentation, pre-existing lymphocytes that bear that antigen receptor are merely selected because they can bind with that antigen.
    • Following T cell maturation, naive T cells circulate through the circulatory and lymphatic systems of the body until presented with an antigen for which they bear the receptor.
    • Following antigen presentation, the T cell is activated and begins to differentiate.
    • The most common subsets are Th1, which mediates cyotoxic T cell activity through cytokine release, and Th2, which presents antigens to B cells.

  • Lymphoid Cells

    • T cells and B cells irecognize specific "non-self" antigens during a process known as antigen presentation with MHC class II (usually done by dendritic cells).
    • Once they have received an antigen, the cells become specifically tailored to eliminate and inhibit the pathogens or pathogen-infected cells that express that antigen.
    • They present antigens to B cells, produce cytokines that guide cytotoxic T cells, and activate macrophages.
    • The lymphocytes involved in adaptive immunity (B and T cells) differentiate further after exposure to an antigen, which occurs in the lymph nodes during antigen presentation from the dendritic cells.
    • The fully differentiated B and T cells are specific to the presented antigen and work to defend the body against pathogens associated with that antigen.

  • Clonal Selection and B-Cell Differentiation

    • B cells primarily function to make antibodies against antigens, act as antigen-presenting cells (APCs), and eventually develop into memory B cells to provide long-term immunity.
    • However, B cell recognition of antigens is not the only element necessary for B cell activation.
    • B cells that have not been exposed to antigen, also known as naïve B cells, can be activated in a T cell-dependent or independent manner.
    • T cell independent activation occurs when antigens directly bind to B cell themselves, usually through cross-linking the antigen to the B cell receptor or receiving the antigen with a toll-like receptor.
    • Clonal selection is a theory stating that B cells express antigen-specific receptors before antigens are ever encountered in the body.