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).

  • Dendritic Cells

    • Dendritic cells are immune cells that function to process antigens and present them to T cells.
    • The function of epithelial dendritic cells is to capture microbial protein antigens and to transport the antigens to draining lymph nodes.
    • During their migration to the lymph nodes, the dendritic cells mature to become extremely efficient at presenting antigens and stimulating naive T cells, hence their classification as antigen presenting cells.
    • Mature dendritic cells reside in the T cell zones of the lymph nodes, and in this location they display antigens to T cells.
    • The ultimate consequence is priming and activation of the immune system for attack against the antigens which the dendritic cell presents on its surface.

  • 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 occurs.
    • 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 into a form in which the antigenic determinant can be recognized by the T cell receptor.
    • Antigen processing occurs within an APC that phagocytizes an antigen and then digests it through fragmentation (proteolysis) of the antigen protein, association of the fragments with MHC molecules, and expression of the peptide-MHC molecules at the cell surface where they can be 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 virally infected cells.

  • Classes of T Cells

    • T cells play a central role in cell-mediated immune response through the use of the surface T cell receptor to recognize peptide antigens.
    • These structures help recognize antigens only in the form of peptides displayed on the surface of antigen-presenting cells.
    • These include naive T cells that recognize antigens and are activated in peripheral lymphoid organs.
    • Memory T cells are an expanded population of T cells specific for antigens that can respond rapidly to subsequent encounter with that antigen and differentiate into effector cell to eliminate the antigen.
    • T cells promote the killing of cells that have ingested microorganisms and present foreign antigens on their surface.

  • Antigen-presenting Cells: B and T cells

    • Meanwhile, T cell receptors are responsible for the recognition of pathogenic antigens by T cells .
    • Unlike B cells, T cells do not directly recognize antigens.
    • Instead, they recognize antigens presented on major histocompatibility complexes (MHCs) that cells use to display which proteins are inside of them.
    • If a cell is infected, it will present antigenic portions of the infecting pathogen on its MHC for recognition by T cells, which will then mount an appropriate immune response.
    • Unlike antibodies, which can typically bind one and only one antigen, T cell receptors have more flexibility in their capacity to recognize antigens presented by MHCs.

  • 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.

  • Clonal Selection and T-Cell Differentiation

    • There are many different types of antigens in the world, and T and B cells are able to respond to nearly all of them 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 system of the body until they are presented with an antigen that they bear the receptor for.
    • 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.

  • Humoral Immune Response

    • Each B cell initially produced has only one kind of antibody (antigen receptor), which makes every B cell unique.
    • When a B cell encounters the antigen that binds to its receptor, the antigen molecule is brought into the cell by endocytosis, reappearing on the surface of the cell bound to an MHC class II molecule.
    • This activation of the helper T cell occurs when a dendritic cell presents an antigen on its MHC II molecule, allowing the T cell to recognize it and mature.
    • The antigen-antibody complex stimulates the complement system described previously, destroying the cell bearing the antigen.
    • B cell receptors, containing antibodies (termed antigen-binding site in the picture) are embedded in the membranes of B cells and bind a variety of antigens through their variable regions.

  • Clonal Selection and Tolerance

    • Central tolerance is distinct from periphery tolerance in that it occurs while cells are still present in the primary lymphoid organs (thymus and bone-marrow), prior to export into the periphery.
    • The cells with useful receptors are preserved, and many potentially harmful, self antigen-reactive cells are eliminated by processes of selection induced by antigen receptor engagement .
    • Negative selection is the process that eliminates developing lymphocytes whose antigen receptors bind strongly to self antigens present in the lymphoid organs.
    • Both developing B cells and T cells are subject to negative selection during a short period after antigen receptors are expressed.
    • Foreign antigen 6.