HOST DEFENCE 2 Flashcards
What’s the role of TH / CD4+ cells?
Recognise antigens presented on Class II MHC (Major Hisrocompatibilty Complex)
What are the three antigen presenting cells?
- Dendritic cells
- B cells
- Macrophages
What are the different types of TH/ CD4+ T cells and what are their functions?
- TH1 - stimulates cell mediated immunity (CDI)
- TH2 - stimulate the growth of specific plasma cell and antibody secretion
What’s the role of Tc or CD8+ T cells?
- Recognise Antigen presented on class I MHC.
- Trigger cytotoxicity (Cell Mediated Immunity)
All nucleated cells in the body produce MHC Class I molecules. True or false?
True
What’s the function of B lymphocyes?
Differentiate to plasma cells which produce antibodies (stimulated by cytokines)
Describe the structure of antibodies/ immunoglobulins? (6)
- Tetramer of two light chains and two heavy chains
- Light chains are two types - the lambda and kappa families
- Heavy chains form a single family
- Each chain has an N-terminal variable region (V) and a C-terminal constant region (C)
- The V domain recognizes antigen
- The C domain binds to specific receptors present in cells of the immune system such as macrophages
What’s the function of antibodies? (4)
- Opsonisation - antibodies bind to the pathogen, this attracts phagocytes
- N terminal binds to the antigen
- Fc portion of the antibody binds to an Fc receptor on the phagocyte, facilitating phagocytosis
- Neutralisation - ability of the antibody to prevent the interaction between the pathogen and the cell
- Complement Activation
- Antibody dependent Cytotoxicity - antibody bound to pathogen interacts with Fc receptors on the NK cell = leads to release of cytoplasmic granules containing perforin and granzymes.
Where are dendritic cells found?
Found in thymus, lymph nodes and spleen (lymphoid organs)
What’s the function of dendritic cells?
Present the antigen or bring it to the lymphoid organs where an immune response is initiated = informing T cells that there is an infected cells
What are the different types of specific acquired immunity and what microbes do eliminate?
- Humoral immunity - extracellular microbe
- Cell-mediated immunity - intracellular microbe (phagocytosed microbes or microbes replicating within infected cells)
What lymphocytes are involved in humoral immunity?
B lymphocyte
What lymphocytes are involved in cell-mediated immunity? (2)
- Helper T lymphocytes - phagocytosed microbes
- Cyotoxic lymphocytes - microbes replicating within infected cell
How are infected cells killed by Tc lymphocytes?
- CTL precursors are activated
- TCR-MHC mediated recognition of target cells and re-orientation of the killing machinery on target cell through polarisation (lytic granules are orientated where MHC class I engages with TCR)
- lytic granules within T cell fuse with cell membrane releasing contents into small gap between T cell and target cell = cytotoxins + pores created on the cell membrane
- CTL then dissociates from the target = not affected
- the release of perforin pokes holes in cell = allows entry of Granzyme B = pathogen is killed by apoptosis
What are the three characteristics of vaccinations?
- Vaccine immunogenicity
- Vaccine efficacy
- Vaccine effectiveness
What is meant by vaccine immunogenicity?
The ability to induce antibodies
What is meant by vaccine efficacy?
Reduction in incidence between those who have been vaccinated and those who haven’t
What is meant by vaccine effectiveness?
The ability of a vaccine to protect a community
Describe the 5 different types of vaccines
- Killed Virulent Organism: Pathogen killed but antigen intact
- e.g. Whooping cough
- Live Attenuated: Strain doesn’t cause disease but still elicits an immune response
- e.g. Rubella
- Modified Toxins: Toxin treated with heat/chemicals, no symptoms experienced but immune response is triggered
- Diphtheria
- Isolated Antigens: Antigen injected to elicit immune response
- Influenza
- Genetically Engineered Antigens: Antigen is isolated and genetically engineered
- Hepatitis B
What affects the response to a vaccine? (7)
- Antigen content (e.g. live vaccines have higher content)
- Protein content (results in increased antibody content)
- Adjuvants present
- Type of antigen
- Dosage intervals - Longer intervals = more MHC interaction
- Genetics
- Age
How do viruses replicate? (8)
- Adsorption: the attachment of the extracellular virus particle to the surface of the host cell
- Penetration: virus fuse their envelope with the plasma membrane of the host cell and move into the cystol (endocytosis)
- Uncoating: is broken down and viral genome is released into the cytoplasm.
- Transcription: the production of viral mRNA (enzymes that are required are in the nucleocapsid)
- Translation: the production of viral polypeptides from viral mRNA
- Replication
- Assembly: the newly replicated viral genes are encapsidated.
- Egress: the release of virus from the infected cell
How does the immune system identify virally infected cells?
- The proteases of the host cell break down the viral products
- These bind to MHC class 1 (if epithelial cell) in the endoplasmic reticulum
- They are transferred onto the surface of the epithelial cell and the viral antigen is displayed on the surface.
What is the first response against the viral infection?
Non-specific.
Cytokines produced include IFN-alpha, IFN-beta, TNF-alpha and IL-12 (act on target cells to inhibit viral replication, not the virus)
What is the second response against a viral infection? (After cytokines)
- NK mediated killing of infected cells
