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Complement System01:27

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The complement system is a group of approximately 20 plasma proteins that strengthen the body's defenses against infections through opsonization, inflammation, and cell lysis. Opsonization involves coating pathogens with complement proteins, making them more recognizable and facilitating phagocyte engulfment. Certain complement proteins induce inflammation that attracts immune cells to the site of infection. Cell lysis involves the destruction of pathogens through the formation of a...
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Hypersensitivity Reactions: Immune-Complex Reactions01:19

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Type III hypersensitivity reactions occur when antigen–antibody complexes form and activate the complement system. Normally, these complexes help the clearance of antigens by phagocytes and red blood cells. However, when large numbers of immune complexes are present, they can deposit in tissues—particularly in the walls of blood vessels—leading to inflammation and tissue injury. These deposits trigger complement activation and neutrophil recruitment, resulting in serum...
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When T cells with CD4 markers are activated, they give rise to two types of effector cells: helper T cells and regulatory T cells. Meanwhile, T cells with CD8 markers differentiate into effector cytotoxic T cells. The differentiation of CD4 T cells into helper T cell subsets, such as Th1, Th2, and Th17 cells, is dependent on the antigen type, antigen-presenting cell, and regulatory cytokines.
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T cells are integral to our adaptive immune system, recognizing and effectively responding to foreign antigens. T cell activation and clonal selection are pivotal in orchestrating this immune response. This article elucidates these mechanisms, detailing the roles of cluster of differentiation (CD) markers, major histocompatibility complex (MHC) molecules, costimulatory signals, and the process of clonal selection.
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Type II hypersensitivity involves IgG and IgM antibodies targeting cell surface antigens, leading to cell destruction. This can occur through complement activation, antibody-dependent cell-mediated cytotoxicity (ADCC), or acting as opsonins for phagocytosis. When excessive, these reactions cause significant tissue damage.Drug-induced hemolytic anemia is a common example, where drugs like penicillin or cephalosporins bind to red blood cells, forming drug-protein complexes. These complexes...
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High-resolution Melting PCR for Complement Receptor 1 Length Polymorphism Genotyping: An Innovative Tool for Alzheimer's Disease Gene Susceptibility Assessment
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Human complement C3 deficiency: Th1 induction requires T cell-derived complement C3a and CD46 activation.

Arije Ghannam1, Jean-Luc Fauquert2, Caroline Thomas3

  • 1Université Joseph Fourier, GREPI/AGIM CNRS FRE3405, Grenoble, France.

Molecular Immunology
|December 11, 2013
PubMed
Summary
This summary is machine-generated.

Human T helper type 1 (Th1) immunity relies on complement system fragments C3a and CD46. These pathways regulate T cell receptor signaling, impacting IFN-γ production and Th1 cell function.

Keywords:
C3 deficiencyC3aComplementT cell effector response

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Area of Science:

  • Immunology
  • Complement System Biology

Background:

  • Human T helper type 1 (Th1) responses are crucial for effective defense mechanisms.
  • T cell activation requires T cell receptor (TCR) and co-stimulator engagement, alongside additional receptor pathway stimulation for effector induction.
  • Complement regulator CD46 engagement by C3b is necessary for IFN-γ production, as evidenced by Th1 deficiency in CD46-deficient patients.

Purpose of the Study:

  • To investigate the role of the anaphylatoxin C3a receptor (C3aR) in human Th1 responses.
  • To determine if complement fragments C3a and CD46 signaling are integral to Th1 immunity.
  • To explore the impact of complement system on interleukin-2 receptor (IL-2R) assembly and Th1 effector function.

Main Methods:

  • Utilized T cells from C3-deficient patients to assess Th1 and Th2 responses.
  • Analyzed CD4(+) T cells for expression of CD25 and CD122 in C3-deficient individuals.
  • Investigated the co-expression of IL-10 in Th1 cells following C3a and CD46 engagement.

Main Results:

  • Normal Th1 responses depend on signals mediated by the C3aR, in addition to CD46.
  • Th1 induction is impaired in C3-deficient patients, while Th2 responses remain unaffected.
  • C3-deficient CD4(+) T cells exhibit reduced expression of CD25 and CD122, indicating impaired IL-2R assembly.
  • Both C3a and CD46 engagement regulate IL-10 co-expression in Th1 cells, suggesting a role in the Th1 contraction phase.

Conclusions:

  • C3aR and CD46 activation, through intrinsically generated ligands, are integral to human Th1 immunity, but not Th2 immunity.
  • Complement fragments play a critical role in regulating Th1 effector responses, including IFN-γ production and IL-2R assembly.
  • The complement system, via C3aR and CD46, influences both the induction and contraction phases of Th1 immune responses.