Antibody- and cell-mediated effector mechanisms Flashcards
(15 cards)
What are the two main components of the adaptive immune system?
Humoral immunity and cellular immunity
Humoral immunity involves antibodies in cell-free fluids, while cellular immunity does not involve antibodies.
What does cell-mediated immunity (CMI) involve?
Production of antigen-specific cytotoxic T-lymphocytes, activated macrophages, activated NK cells, and cytokines
CMI protects the body by activating immune cells to destroy infected or foreign cells.
How does cell-mediated immunity protect the body?
By activating CTLs to lyse invading cells, activating macrophages and NK cells to destroy intracellular pathogens, and stimulating cytokine production
This involves a response to microbes that survive in phagocytes and infect non-immune cells.
What are the steps involved in T cell-mediated immunity?
- Antigen encounters antigen presenting cells
- Naïve T-cells recognize antigen epitope and become activated
- Clonal selection
- Activated T-cells proliferate (clonal expansion)
- T-cells differentiate into effector and memory T-cells
Effector cells include cytotoxic T cells (CTLs).
What is the role of cytotoxic T-lymphocytes (CTL)?
They recognize infected cells expressing MHC-I/antigen epitope and initiate destruction through apoptosis
CTLs can have up to 250,000 MHC-I/epitope complexes on their surface.
What are the two pathways through which CTLs induce cell death?
- Intracellular granules
- Fas Ligand/Fas interactions
Both pathways lead to apoptosis of the infected cell.
What proteins do CTLs release to trigger apoptosis?
Perforins and granzymes
Perforins form pores in the infected cell, allowing granzymes to enter and activate apoptotic enzymes.
How do CTLs recognize and destroy infected cells?
Through T-cell receptor (TCR) recognition of MHC class I/epitope complex
CTLs also express CD8, which assists in antigen recognition.
What is the role of Th1 lymphocytes in activating macrophages?
Th1 lymphocytes bind to peptide/MHC-II complexes on macrophages and secrete interferon-gamma (IFN-gamma)
This activation enhances the macrophage’s ability to kill microbes and recruit other immune cells.
What is the primary role of NK cells in cell-mediated immunity?
To target cells that cytotoxic lymphocytes do not recognize, especially those that downregulate MHC-I
NK cells recognize stressed cells by their expression of stress proteins.
How do NK cells decide whether to kill a cell?
Using a dual receptor system to assess the presence of stress proteins and MHC-I on the infected cell
If MHC-I is present, it inhibits the kill signal; otherwise, NK cells may kill the cell.
What is Koch’s phenomenon?
Inoculation of an un-immunized guinea pig with a lethal dose of mycobacterium tuberculosis results in death, while a sublethal dose induces immunity
In previously immunized guinea pigs, a local reaction occurs when re-exposed to a lethal dose.
What is the Mantoux test used for?
To detect infection with mycobacterium tuberculosis by injecting a tiny amount of its protein into the skin
A hard red nodule develops if the person has been infected, indicating a cell-mediated immune response.
What is transplant rejection?
Occurs when the immune system attacks a transplanted organ identified as foreign
It can be reduced by tissue typing and immunosuppressant drugs.
What is the significance of HLA mismatching in transplant rejection?
Mismatched HLA can lead to the immune system recognizing the transplant as foreign and attacking it
A perfect match between all alleles is rare, increasing the risk of rejection.
