The Immune System Flashcards
What are the different components of innate immunity
Soluble factors such as antibacterial factors and complement system.
Cellular factors such as scavenger phagocytes
Name and describe different antibacterial factors
Lysozyme - These are enzymes present at mucosal surfaces which breakdown the cell wall of gram positive bacteria.
Lactoferrin - Protein found at mucosal surfaces. Bonds to iron, reducing the amount of soluble iron which inhibits the growth of bacteria
What are the different ways of activating complement pathways?
Classical pathway which is activated by antigen-antibody complexes.
Alternative pathways which is activated by pathogen surfaces.
Lectin pathways which is activated by lectin binding to pathogen. (least important pathways)
What occurs as a result of the complement pathway?
- Recruitment of inflammatory cells,
- Opsonization of pathogens
- Killing of pathogens
Explain in more detail what occurs when the complement pathways is activated
C3 is activated into C3a (responsible for inflammation) and C3b (responsible for opsonization and phagocytosis). Activated C3 also activates C5 which leads to the membrane attack complex forming (causing lysis).
What are the primary cells of the innate immune system
-Macrophages,
-Neutrophils,
- Eosinophils,
- Basophils.
Describe features of macrophages
They have pattern recognition receptors (toll-like receptors) on the surface of the cell, which are activated by pathogens resulting in production of cytokines. They are responsible for clearance of pathogens, antigen presentation to T cells via MHC2 and produce cytokines to recruit other immune cells.
Called monocytes in the blood.
Describe features of Neutrophils.
- Attracted towards bacterial products, chemokines and complement components.
- Phagocytose and destroy bacteria
- Can degranulate which causes the release of toxic granules (contain lots of DNA resulting in multilobed nucleus)
- Die locally producing pus.
Describe features of eosinophils
- Migrate in response to chemokines,
- Degranulate causing the release of toxins onto the surface of parasites.
- Produce cytokines which drives inflammation
- Pathological role in allergy
Describe features of basophils (blood)/mast cells (in tissue)
- Degranulate causing release of pre-formed granules containing cytokines and mediators (eg histamine),
- Release cytokines to drive inflammation.
Describe features of dendritic cells.
- Survey the contents of the extra cellular fluid.
- Phagocytose pathogens but instead of destroying the pathogen it presents the antigen.
- Migrate to lymphnodes where they will present the antigen
- Antigen presentation to CD4 cells which activates the adaptive immune system.
Describe an overview of the adaptive immune system.
Two pathways:
Humeral immune response results in the activation of |B cells causing the release of antibodies.
Cellular immune response which results in the activation of CD4 T cells (helper T cells which direct B cells and CD8 T cells via production of cytokines) and CD8 T cells (Killer cells which targets intracellular pathogens like viruses).
Describe the structure and function of antibodies.
- Consist of 2 light and 2 heavy chains. With a fab region which binds to antigen and the Fc region which binds to phagocytes.
- They opsonise for phagocytosis, activate complement for lysis and neutralise toxins and pathogen binding sites.
Name and describe the different antibody isotypes
IgM - Main antibody in primary and early immune response. It has a low affinity but highly affective at complement activation
IgG - Main antibody of secondary immune response. Activates complement and opsonizes phagocytosis. Only antibody that crosses placenta so only antibody that is responsible for neonatal immune response.
IgA - Lines mucosal membranes and prevents the binding of pathogens (antiseptic paint)
IgE - High affinity for mast cells for has a role in allergy
What are the differences between primary and secondary immune responses
Primary (activation of B cells) - slower and smaller immune response. Primarily IgM then IgG.
Secondary - Faster and larger immune response. Occurs due to memory B cells which therefore respond faster upon secondary exposure to pathogen. IgG throughout response making it far more effective.
What are the functions of CD4 T cells.
Optimise B cell response:
- T cells directly stimulate the growth and development of B cells.
- Permits development into memory B cells,
- Triggers isotype switching from IgM to IgG, IgA and IgE.
- Causes affinity maturation
Describe features of T cell receptors?
They are found on the surface of T cells and ONLY recognises antigens (only needs short peptide lengths) when it is presented by a MHC molecule
How does the immune system prevent autoimmunity?
- B cells develop in the bone marrow. If B cell strongly binds to self antigens in the bone marrow then the B cell dies via apoptosis before release.
- T cells originates in bone marrow then migrate to thymus. Again, if strongly binds to self antigens then T cell dies via apoptosis in thymus
- Activate of both B and T cells requires a co-stimulate (Danger signal) so without this, then the cell is likely to become anergic.
What are the different MHC molecules and their features.
Class 1 MHC - Found on all nucleated cells and presents intracellular antigens only to CD8 T cells.
Class 2 MHC - Found only on antigen presenting cells and presents extracellular antigens only to CD4 T cells.
What are the roles of different CD4 T cells?
They produce different combinations of cytokines in different contexts.
Th1 Cells - secrete interferon gamma. Activates macrophages
Th2 Cells - IL 4 (and others), Promote antibodies. host defence against helminth and allergies.
Th17 - IL-17 - Promote mucosal immunity and inflammatory disorders.
T regulatory cells - regulates function of other immune cells (can stop immune response)
What are the primary and seconary immune organs?
Primary - Bone marrow and thymus.
Secondary - Lymph nodes, spleen, mucosal associated lymphoid tissue (MALT - mini lymphnodes)
What are germinal centres?
Areas within a lymphnodes where replication of B/T cells occurs
What is the important functions of the spleen?
Responded to encapsulated organisms and blood borne pathogens. It also removes dead/old RBCs
