Partridge L1-10 Flashcards
What is immunology?
Study of the immune system. Provides defence against infection, distinguishes between self and non self and recognises danger signals.
What are the two types of the immune system?
Innate and adaptive
What are characteristics of innate immunity?
Broad specificity, not affected by prior contact. Immediate response is rapid and within hours.
What are characteristics of adaptive immunity?
Highly specific and enhanced by prior contact. Response is slow and takes days to weeks.
What is involved in innate immunity?
Barriers (physical and chemical), soluble proteins (complement, interferons), local and systemic responses (inflammation, fever), leukocytes.
What is involved in adaptive immunity?
B and T lymphocytes. B cells respond by secreting soluble antibodies in humoral immunity. T cells develop into cytotoxic T cells that kill infected host cells (important in viral infections) or helper T cells which secrete cytokines acting on other cells, in cell mediated immunity. Both B and T cells develop into memory cells.
How is infection recognised in adaptive immunity?
B and T lymphocytes express specific antigens receptors.
How is infection recognised in innate immunity?
Pattern recognition receptors recognise pathogen associated molecular patterns on cells of innate immune system. PAMPs include LPS or peptidoglycan and are conserved due to being essential for survival.
What is the clonal selection hypothesis?
B lymphocytes have a preformed receptor on the surface that recognises a particular microbe. Upon contact with an antigen it undergoes clonal selection where the parent divide as clones. Those that recognise “self” are deleted early in development and so they cannot cause harm to body. Healthy lymphocytes can then go onto become plasma cells and memory cells.
What is primary lymphoid tissue?
Where lymphocytes reach maturity and acquire their specific receptors (bone marrow + thymus).
What is secondary lymphoid tissue?
Where mature lymphocytes are stimulated by antigens.
What do dendritic cells in the lymph node?
Presents microbe to T cell and if it has the right antigen it will differentiate into Helper or Cytotoxic. Same with B cells but these will form plasma cells.
What do the elements of the innate immune system do?
Barriers = prevent establishment of infection.
Preformed mediators = Proteins with broad specificity that damage pathogens, induce inflammation or recruit innate immune cells.
Innate immune cells = Recognise and activated by pathogen, eliminated pathogen, cell communication and activate/steer adaptive immune response.
How do mechanical barriers prevent infection?
Secretes chemicals, anti microbial and commensals to create an unfavourable environment for pathogens.
What are examples of preformed mediators?
Lysozyme. Antimicrobial peptides. Complement.
What is lysozyme?
Present in secretions such as tears, saliva and mucous. Breaks a bond in peptidoglycan so more active against gram +ve bacteria where peptidoglycan is exposed.
What are antimicrobial peptides?
Such as defensins which are evolutionary ancient. Produced by epithelial cells and neutrophils. Cationic meaning they insert into pathogenic membranes and disrupt lipid bilayers.
What is complement?
Discovered as a heat – sensitive substance that complemented antibodies in killing bacteria. There are >20 soluble proteins found in the blood and other bodily fluids. Components usually inter but activated by presence of pathogens or antibody bound to the pathogen. Proenzyme is activated on by infection forming a working enzyme which can further go on to form other proenzymes and enzymes.
What is the classical pathway for complement activation?
C1,4,2,3,5,6,7,8,9
What do activated complement components act as?
Proteases so act on one another to generate a large and smaller fragment. C3 -> C3b + C3a. Where b denotes the bigger fragment and a denotes the smaller fragment. Cleavage of C3 exposes a reactive thioester in C3b which can covalently bind to adjacent proteins.
What are the three pathways for complement activation?
Classical = C1,4,2,3,5,6,7,8,9.
Mannose binding lectin pathway = MBL binding to mannose.
Alternative pathway = LPS to factor B to factor D to factor P.
What is the alternative pathway for complement activation?
If C3b generated binds to LPS on a pathogen surface, factor B binds. Factor B is cleaved by factor D -> C3 convertase (C3bBb). The C3bBb convertase is stabilised by factor protein P (properdin). This became known as the alternative pathway. C3b generated by classical/MBL pathway can also bind factor B.
What are the three major biological activities of complement?
- C5a (C3a) recruits phagocytes and induces inflammation. They act as chemo attractants and anaphylatoxins. Phagocytes have C5a and C3a receptors and undergo chemotaxis in response to C5a/C3a peptide.
- C3b promotes opsonisation. Pathogens coated with C3b peptides are recognised by phagocytosis with C3b receptors, facilitating binding and phagocytosis.
- C5b – C9 form the Membrane Attack Complex, leading to lysis. Activation of C5b – C9 results in C9 polymerisation, forming a pore in the membrane, disrupting it and killing the pathogen. This is important in the killing of gram negative bacteria.
Why is complement inactivation important?
To prevent host damage