Bacterial story board Flashcards
How does the body fight a bacterial infection?
1) There is a break in the epithelial surface, which allows the bacteria to enter and proliferate. The first stage of immune response is innate immunity, which is non-specific and responds rapidly
2) Surface lipopolysaccharides on the bacteria activate the alternative complement pathway or the Mannan binding lectin pathway leading to bacteria cell lysis. Complement activation also leads to mast cell activation, opsonisation and chemotaxis. C-reactive protein can bind to bacteria and activate complement
3) Mast cell degranulation causes increased blood flow and leaky blood vessels. You get oedema in the area and local irritation
4) Neutrophils drawn to area by complement, bacteria products and chemokines. They adhere to the endothelial cells and marginate into infected tissue
5) Opsoniszed bacteria are phagocytosed and killed by neutrophils. Dendritic cells engulf and internalize bacteria. They then migrate to a lymph node via the lymphatics
6) T cells are recruited to the lymph node by dendritic cells. The dendritic cells present the bacterial peptide naïve T-helper cells on their MHC II molecules to activate T-cells. The dendritic cells can activate T helper 1 and T helper 2 cells
7) Activated T helper 2 cells cause B cells to become plasma cells and produce antibodies. Initially the IgM class of antibodies are produced followed by class switching to IgG or IgA
8) Early antibody production is of the IgM class. There are five binding sites on IgM which enhance the binding efficiency. IgM is a good opsonin and activator of the classical complement pathway. Opsonized bacteria are engulfed by phagocytes
9) In the resolution of an infection, bacterial debris is removed by neutrophils or by antibody as soluble immune complexes
Characteristics of innate immunity
Non-specific and responds rapidly
What do surface lipopolysaccharides do?
Activate the complement pathway
What is a zymogen?
Complement proteases that are activated by proteolytic cleavage
What do zymogens do?
Trigger inflammation
What part do zymogens play in the enzyme-triggered cascade?
Active complement enzyme cleaves its substrate into its active enzymatic form
This in turn cleaves and activates the next zymogen in the pathway
What is the end result of the pathways?
C3 converts
How does the complement system protect against infections?
?Generates large numbers of activated complement proteins to bind to pathogens and opsonise them
Where do mast cells come from?
Haemopoetic stem cells of bone marrow
How do mast cells change when they mature?
They acquire secretory granules that become filled with substances like histamines and serotonin
What do mast cells do?
Synthesis of inflammatory mediators
Recruit inflammatory cells through secretion of cytokines
Promote migration of dendritic cells and T-cells to lymph nodes
Present bacterial antigens through MHC I complex
What do MHC II cells do?
CD4 or T-helper cells
What MHC I cells do?
CD8 or cytotoxic T cells
How are neutrophils initiated to phagocytose?
Bacteria must be decorated opsonins
What happens when pathogens are phagocytose?
Parts are displayed on MHC II
