Intro Flashcards
What is immunology?
The study of the immune system and defence against disease
What are the 3 main components of our multi-layered defence?
Barriers (mechanical, chemical, microbiological)
Innate immunity
Adaptive immunity
State the mechanical and chemical defences provided by the skin, gut, eye/nose/oral cavity
Responses can be divided into stages
- Pathogens adhere to epithelium
- Local infection, penetration of epithelium
- Local infection of tissues
- Adaptive immunity
Describe the sequential protection against infection
- Normal flora, local chemical factors, phagocytes (especially in the lungs)
- Wound healing, induced antimicrobial proteins and peptides, phagocytes and complement destroy invading microorganisms
- Complement, cytokines, chemokines, phagocytes, NK cells. Activation of macrophages, Dendritic cells migrate to lymph nodes to initial adaptive immunity. Blood clotting helps limit the spread of infection
- Infection cleared by specific antibody, T-cell dependent macrophage activation and cytotoxic T cells
How are pathogens recognised and destroyed?
- Bacterial cell surface induces cleavage and activation of complement
- One complement fragment covalently bonds to the bacterium, the other attracts an effector cell
- The complement receptor on the effector cell binds to the complement fragment bacterium
- The effector cell engulfs the bacterium, kills it and breaks it down
Describe the process of an inflammatory response
- Healthy skin is not inflamed
- Surface wound introduces bacteria, which activate resident effector cells to secrete cytokines
- Vasodilation and increased vascular permeability allow fluid, protein and inflammatory cells to leave blood and enter tissue
- The infected tissue becomes inflamed, causing redness, heat, swelling and pain
Describe pathogen recognition- Innate Immune receptors
- PRR on cells recognise PAMP on pathogens
- Mannose R, Scavenger R and Glucan R are all lectins and recognise carbohydrates on microbial surfaces
Many others including:
- Toll-like receptors
- NOD-like receptors
- Complement receptors e.g. CR3 binds iC3b (from complement activation)
- CD14 binds LPS
What are Toll-like receptors (TLR) and how do they sense infection?
TLR
- Family of signalling receptors
- Recognise different pathogens
- Tailor innate immune responses to WHAT and WHERE
- TLR signalling switches on cytokine production
- This informs adaptive immunity
- TLR also play a central role in the activation of MØ and NØ
Can you identify these important immune cells?
- Neutrophil
- Monocyte
- Mast cell
- Lymphocyte
- Plasma cell
- Macrophage
- Dendritic cell
What are the granulocytes?
Neutrophils
Eosinophils
Basophils
Monocytes
What are the adaptive immune cells?
What role do macrophages and dendritic cells fulfill?
They bridge adaptive innate and adaptive responses. Linking innate and adaptive immune responses via Ag presentation on MHC Class II.
Innate immunity can limit infection but it needs some help to eradicate infection from
the adaptive immunity (3rd line of defence)
What is involved in the adaptive immunity?
–Lymphocytes – B cells and T cells
–Unique system of recognition
–Adapts to pathogens (highly specific)
–Long-lasting (memory cells)
Describe pathogen recognition- adaptive immune receptors
How are the receptors made?
Each lymphocyte expresses just one molecular type of receptor
B cells – BCR (membrane immunoglobulin)
T cells – TCR
The receptors are made by gene rearrangement so we all have millions of different specificities
Describe the selection of lymphocytes by a pathogen
- Progenitor cells with millions of different specificities
- Detection of a foreign antigen (pathogen) by the specific lymphocyte –CLONAL SELECTION
- Activation > proliferation & differentiation to many effector cells specific for the infection –CLONAL EXPANSION
- Infection terminated
Describe the activation of adaptive immune response in a draining lymph node
MHC I binds to
CD8 T Cell
MHC II binds to
CD4 T Cell
T cells function by making contact with other cells T cells function by making contact with other cells
Antibodies just keep getting better to tailor the response we need. How is this achieved?
- IgM is the first antibody made against an infecting pathogen
- Somatic hypermutation selects for antibodies that bind more tightly to the pathogen
- Switching antibody isotype to IgG allows delivery of the pathogen to phagocytes
