questions 4

Cells of the Immune System

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Topic updated on 07/12/17 12:54pm

Overview
 

This illustration highlights the basic development of various blood cells from hematopoietic stem cells.

 
Introduction
  • The immune system involves cells from two major lineages including
    • lymphoid cells derived from a lymphoid progenitor such as
      • natural killer (NK) cells
      • T-lymphocytes
      • B-lymphocytes
    • myeloid cells derived from a myeloid progenitor such as
      • mast cells
      • basophils
      • neutrophils
      • eosinophils
      • monocytes
      • macrophages
  • These cells carry out many of the major roles of the immune system including
    • phagocytosis of invading microbes
    • secretion of the protein components of humoral immunity such as
      • antibodies
    • production of toxic substances such as
      • reactive oxygen species
    • direct cytotoxic signals through receptor based interactions
Lymphoid Cells
  • Lymphoid cells can broadly be divided into four classes including
    • NK cells that kill cells without major histocompatability complexes (MHC)
    • T-cells that can be further subdivided into
      • killer T-cells that are directly cytotoxic
      • helper T-cells that enable other immune functions
      • regulatory T-cells that maintain immune tolerance
    • B-cells that mediate humoral immunity
Lymphoid Cell Types
Feature NK Cells B Cells Killer T
Helper T
Regulatory T
Function
  • Kill cells lacking MHC
  • Secrete antibodies
  • Kill infected cells
  • Enable other immune cells
  • Suppress immunity
Surface proteins
  • CD56
  • MHC receptor
  • CD19, 20, and 21
  • CD40
  • CD2
  • CD8
  • CD2
  • CD4
  • CD4
  • CD25
Secreted proteins
  • Perforin
  • Granzymes
  • Antibodies
  • Toxic compounds
  • Diverse cytokines
  • IL10
  • TGF-B
  • Helper T-cells (CD4+ cells) can be further subdivided into classes based on function
Helper T-Cell Subtypes
Feature Th1 Th2
Th17
Function
  • Promote cell based immunity
  • Activate macrophages and cytotoxic T-cells
  • Promotes humoral immunity
  • Recruits eosinophils as part of parasite defence
  • Activate neutrophils
Differentiation
  • IFN-γ
  • IL-12
  • IL-2
  • IL-4
  • IL-6
  • TGF-β
Associations
  • Granuloma formation
  • Tuberculous leprosy 
  • Lepromatous leprosy
  • IgE production by B cells
  • Chronic inflammatory conditions
Secreted Factors
  • IFN-γ
  • IL-2
  • IL-4
  • IL-5
  • IL-13
  • IL-17
  • IL-21
 
Myeloid cells
  • Myeloid cells perform a large variety of innate immune functions including
    • phagocytosis of invading antigens
    • secretion of cytokines and immunoactive proteins
    • clearance of cellular debris
    • presentation of antigens to adaptive immune system
    • alteration of vascular physiology
  • Different innate immune cells are specialized for different functions
 
Myeloid Cell Types
Cell Type Functions and Features
Monocytes
  • Phagocytosis of invading pathogens
  • Differentiates into macrophages
  • Express receptors for the antibody Fc and the complement protein C3b
Macrophages
  • Phagocytosis of pathogens as well as cellular debris
  • Secretion of cytokines
  • Stimulation of the healing response
Dendritic cells
  • Capture of antigens from pathogens
  • Presentation of antigens to adaptive immune cells
  • Called Langerhans cells in skin and mucosa
Neutrophils
  • Secretion of cytokines and signaling molecules
  • Phagocytosis of pathogens
  • Generation of reactive oxygen species
Eosinophils
  • Production of major basic protein
  • Anti-parasitic defence
Basophils
  • Allergic response
Mast cells
  • Production and release of histamine
  • Allergic repsonse


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