Immunology Flashcards
How do gram -ve bacteria activate the complement system?
- Proteases, endotoxins & lipopolysaccharides found in cell wall of gram -ve bacteria activate the complement system by the alternative pathway
- Factors D,B,C3,C5-9 are activated
What does activated complement system result in?
a) release of histamine from mast cells, produce vasodilatation, increase vascular permeability & broncho-constriction
b) attraction of polymorph to site of complement activation
c) phagocytosis is induced because activated complement molecules adhere to marcrophages & polymorphonuclear leukocytes.
d) when C8 & C9 they produce membrane damage by phospholipase activity this damages cell membranes (both bacterial & human) causing cell lysis.
What antibodies are capable of activating the first factors of complement?
IgG & IgM
What activates complement in the early stages of primary infections?
structural components e.g. endotoxin or products e.g. proteases.
What is cell mediated immunity involved in?
- Resistance to infections
- Tumour rejection
- Delayed hypersensitivity states
- Regulation of immune system
What is immunological surveillance?
The immune system recognising mutating clones of neoplastic cells. during organ transplant
What is the role of IgG?
- Major class (75%) in blood serum
- Activates complement
- Neutralisation of toxins & viruses
- Agglutination
- Only Ig that is readily phagocytosed
- Cell mediated cytotoxicity
- Opsonisation
- Crosses placenta imparts passive protection to new-born for 4-6 months
How does IgG act as an opsonin?
substance presents in serum that promotes phagocytosis of bacteria: binds to antigen of bacteria functioning region of antibody and is recognised by constant region by receptors of phagocytes.
What is the role of IgA?
- Main Ig in mucous
- Agglutination
- Antimicrobial
- Does not activate complement
What is the role of IgM?
- 1st Ig in primary response
- Pentameric structure means its effective in activating complement
- Agglutination
- Poor toxin/virus neutralisation strength
- First Ig to be made on foetus at 5 months (raised levels suggest intra-uterine infection e.g. Syphilis or Rubella)
What is the role of IgD?
Found in blood but low levels
- Not secreted but membrane bound
- Marker for B cell maturity
- Cannot activate complement
What is the role of IgE?
Found in very small amounts in serum
- Most attached to mast cells and basophils- release histamine a inflammatory mediator for hypersensitivity
- High levels in allergic individuals
What is Lymphokine?
Non-immunoglobulin polypeptide substances synthesised mainly by T lymphocytes that affects the function of other cells.
May either enhance or suppress an immune response
Facilitate cell proliferation, growth and differentiation and they may act on gene transcription to regulate functuon.
E.g. Interleukin2, 3, migration inhibitory factor and gamma interferon.
What are the two types of effects of lymphokines?
Paracrine effect= local effect acting on cells in itd immediate vicinity
Autocrine effect= action on the same cell that synthesised it
