effector cell

Examples of effector cell in the following topics:

• Immunological Memory

  • As B cells and T cells mature into effector cells, a subset of the naïve populations differentiates into B and T memory cells with the same antigen specificities .
  • A memory cell is an antigen-specific B or T lymphocyte that does not differentiate into an effector cell during the primary immune response, but that can immediately become an effector cell on re-exposure to the same pathogen.
  • As the infection is cleared and pathogenic stimuli subside, the effector cells are no longer needed; they undergo apoptosis.
  • If the pathogen is not encountered again during the individual's lifetime, B and T memory cells will circulate for a few years or even several decades, gradually dying off, having never functioned as effector cells.
  • As a result, memory B cells and plasma cells are made.

• 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.
  • This activation results in the expansion of the antigen-specific lymphocyte pool and the differentiation of these cells into effector and memory cells.
  • Effector cells include helper T cells, and cytolytic or cytotoxic T cells.
  • 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.
  • Distinguish between: naive, effector (helper and cytotoxic), memory and regulatory T cells

• Clonal Selection and T-Cell Differentiation

  • The increased binding affinity may be the reason why memory cells can eliminate a pathogen more rapidly than the original generation of effector cells.
  • Cloned daughter cells differentiate into either effector T cells or memory T cells.
  • Cytotoxic effector T cells are finished, but helper T cells continue to differentiate into individual subsets of helper T cells.
  • Additionally, Th17, which only differentiates from effector cells if certain cytokines are present, are important in regulating and inhibiting T-reg cell activity.
  • The effector cells are short lived for the duration of the adaptive immune response while memory cells are long lived and are the basis of the secondary immune response.

• Macrophages

  • Macrophages are antigen presenting cells that actively phagocytose large particles .
  • In the effector phase of cell-mediated immunity, differentiated effector T cells recognize microbial antigens on phagocytes and activate the macrophages to destroy these engulfed microbes.
  • Most macrophages express high levels of interferon-gamma, a mechanism through which antigen presentation and T cell activation is enhanced.
  • Macrophages are not cells exclusive to the immune system; they also play a central function in many other aspects of embryonic development, homeostasis and wound repair.
  • They respond to local stimuli by producing cytokines that make the endothelial cells more sticky (through the increased expression of cell adhesion molecules such as P-selectin) and so-called chemokines, that promote the directed migration of inflammatory cells.

• Specific T-Cell Roles

  • T helper cells assist the maturation of B cells and memory B cells while activating cytotoxic T cells and macrophages.
  • Differentiation into helper T cell subtypes occurs during clonal selection following T cell activation of naive T cells.
  • They rapidly proliferate to large numbers of effector T cells upon re-exposure to their antigen, thus providing the immune system with "memory" against past infections.
  • Memory T cells comprise two subtypes: central memory T cells (TCM cells) and effector memory T cells (TEM cells), which have different properties and release different cytokines.
  • Effector memory cells may be either CD4+ or CD8+, and will produce either helper or cytotoxic T cells in a secondary immune response.

• Dendritic Cells

  • Dendritic cells are immune cells that function to process antigens and present them to T cells.
  • Mature dendritic cells reside in the T cell zones of the lymph nodes, and in this location they display antigens to T cells.
  • Different subpopulations of dendritic cells may stimulate distinct types of T cell effector responses.
  • Dendritic cells are constantly in communication with other cells in the body.
  • This communication can take the form of direct cell-to-cell contact based on the interaction of cell-surface proteins.

• Plant Pathogens

  • There are four main bacterial pathogenicity factors: cell wall degrading enzymes, toxins, phytohormones, and effector proteins.
  • Cell wall-degrading enzymes: These are used to break down the plant cell wall in order to release the nutrients inside.
  • Effector proteins: These can be secreted into the extracellular environment or directly into the host cell, often via the Type three secretion system .
  • Some effectors are known to suppress host defense processes.
  • Necrotrophic fungal pathogens infect and kill host tissue and extract nutrients from the dead host cells.

• Natural Killer Cells

  • Natural killer cells (or NK cells) are a type of cytotoxic lymphocyte critical to the innate immune system.
  • NK cells differ from Natural Killer T cells (NKT) phenotypically, by origin, and by respective effector functions.
  • Often NKT cell activity promotes NK cell activity by secreting IFNγ.
  • Natural killer cells are not only effectors of innate immunity; recent research has also uncovered information on both activating and inhibitory NK cell receptors, which play roles in maintaining self-tolerance and sustaining NK cell activity.
  • Functions of NK cells include: Cytolytic Granule Mediated Cell Apoptosis; Antibody-Dependent Cell-Mediated Cytotoxicity (ADCC); Cytokine induced NK and CTL activation; Missing 'self' hypothesis; Tumor cell surveillance; NK cell function in adaptive response; NK cell function in pregnancy; and NK cell evasion by tumor cells .

• Development of the Dual Lymphocyte System

  • B cells and T cells are the major types of lymphocytes.
  • Mammalian stem cells differentiate into several kinds of blood cell within the bone marrow.
  • B and T cells) differentiate further after exposure to an antigen; they form effector and memory lymphocytes.
  • Effector lymphocytes function to eliminate the antigen, either by releasing antibodies (in the case of B cells), cytotoxic granules (cytotoxic T cells) or by signaling to other cells of the immune system (helper T cells).
  • Mammalian stem cells differentiate into several kinds of blood cell within the bone marrow.

• Adaptive Immunity and the Immunoglobulin Superfamily

  • Antibodies or Immunoglobulins bind antigens in the recognition phase and the effector phase of humoral immunity.
  • These membrane molecules function as B cell receptors for antigens.
  • The interaction of antigens with membrane antibodies on naive B cells initiates B cell activation .
  • These activated B cells produce a soluble form of immunoglobulin that triggers effector mechanisms to eliminate antigens.
  • When a B cell encounters its triggering antigen, it gives rise to many large cells known as plasma cells.