Introduction to immune response Flashcards
- Describe the importance of both innate and adaptive immune systems - **Describe the differences between innate and adaptive immune systems naming the cells and molecules involved in each** - **List and describe the role of innate protective factors acting as barriers to infection** - **Describe the function of T lymphocytes** - **Describe the function of B lymphocytes** - **Define phagocytosis and describe the function of phagocytic cells.** - **Describe the characteristics of the main phagocy
What is the innate immune response?
What type of response does it induce?
Innate immune response is the immune response we are born with.
It produces a non-specific response
What are the chemical and physical barriers that repel pathogens in the innate immune system?
- Chemical barriers- lysozyme (tears), low stomach pH creating acidic environment
- Physical barriers- Epithelium (skin/gut), cilia lining airways
How does lysozyme acts as a barrier to infection?
- It acts as a mechanism to kill bacteria by hydrolysing their peptidoglycan cell walls , so it’s especially effective against gram-positive bacteria
How does low stomach pH act as a barrier to infection?
The low pH kills most microorganisms that are ingested
What are the key features of the innate immune system?
- Non-specific cells that do not distinguish invaders
- Response occurs within minutes-hours
- No memory cells
- Always respond to pathogen in the same manner
Define phagocytosis
The ingestion of bacteria or other pathogens by phagocytes
What cells are phagocytes?
Monocytes
Macrophages
Neutrophils
Basophils
Eosinophils
Mast cells
Dendritic cells
What is the function of monocytes?
Monocytes reside in blood and tissues to find and destroy pathogens, and eliminate infected cells
What is the function of macrophages?
Recognise pathogen and activate innate immune system
Destroy infectious organisms that enters the body, clear cellular debris and wound healing
What is the function of neutrophils?
Cells that travel to site of infection, where they destroy microorganisms by ingesting them and releasing enzymes that kill them (phagocytosis)
What is the function of basophils?
- Immune surveillance
- Play key role in response to allergies - release histamine which enlarges blood blood vessels to improve blood flow and heal affected area
- Histamine also allows other cells to quickly target and respond to allergen
What is the function of eosinophils?
- Active pathogenic role in inflammation associated with allergic disorders.
What is the function of mast cells?
Contain chemicals such as histamines, heparin, cytokines that play a role in immune restore to certain bacteria and parasites, and other types of immune response
What is the function of dendritic cells?
- They capture, process and present antigens from pathogen to immune cells (T and B cells) and mediate their polarisation into effector cells, therefore these activate the specific (adaptive) immune system
What are the 4 stages of phagocytosis?
Stage 1 - Recognition of the target particle (opsonisation) and chemotaxis
Stage 2 - Signalling to form phagosome
Stage 3- Phagolysosome formation
Stage 4- Oxidative burst
Explain the first stage of phagocytosis, recognition of the target particle and chemotaxis
- Pathogens release inflammatory mediators (inflammatory cytokines, complement proteins etc), called Pathogen Associated molecular patterns (PAMPs)
- Resting phagocytes have pattern recognition receptors (PRRs) that identify PAMP and are activated by these , resulting in circulating phagocytes producing surface glycoprotein receptors, increasing their ability to adhere to inner surface of capillary walls, and move to the site of infection (this is chemotaxis).
- Receptors on the plasma membrane of phagocytes can release opsonin, which coats cells or pathogens so phagocytes become attracted to them (opsonisation)
Explain the second stage of phagocytosis, signalling to form phagosome
- Phagocytic receptors initiate signalling cascades that remodel lipids in the cell membrane and regulate the actin cytoskeleton to extend the cell membrane around the pathogen
- Phagocytic receptors engage in a sequential order and cooperate to complete the formation of the phagosome
Explain the third stage of phagocytosis, phagolysosome formation
- The phagosome fuses with lysosomes
- The membrane changes its membrane composition and contents to turn into a phagolysosome, a vesicle that can release digestive lysosomes to destroy the pathogen. This transformation is phagosome maturation.
- Phagosome maturation consists of successive fusion and fission interactions between the phagosome and endosomes, late endoscopes and finally lysosomes to become a phagolysosome. This is because the phagosome fuses with lysosomes when it becomes a late stage phagosome through interaction with endoscopes.
- At the end, the phagolysosome has a different membrane composition, as granules from lysosomes contain a very acidic and degradative environment, which allows it to kill and digest pathogens
After the pH is sufficiently lowered, azurophilic granules are activated and kill more pathogens
Explain the fourth stage of phagocytosis, phagolysosome maturation
NADPH oxidases oxidise O2 molecules, creating superoxide ions. The ions are converted by superoxide dismutate into H2O2, which then destroys remaining pathogens
- Continues to swallow pathogens before oxidative burst-> Produces highly reactive oxygen e.g. H2O2; destroys proteins, nucleic acids, killing pathogens and the phagocyte
How does phagocytosis remove dead cells?
- Dying cells secrete a ‘find me’ signal, and they expose this signal on their surface.
- Phagocytes ingest the dead cells, direct them to lysosomes, and degrade their cellular components into basic biochemical building blocks: amino acids, nucleotides, fatty acids, and monosaccharides.
- These molecules will be released from the lysosomes and reused to make new macromolecules
What are the cell types in the adaptive immune response?
- T helper cells
- Cytotoxic T cells
- B cells
- Plasma cells
What are the functions and properties of T helper cells?
- Involved in cell-mediated response
- Recognises antigens presented by MHC class II molecules
- Expresses CD4, CD3, TCR, CD28
- Major source of IL-2
- Mediates acute and chronic organ rejection
What are the functions and properties of Cytotoxic T cells?
- Involved in cell-mediated response
- Recognises antigens presented by MHC class I molecules
- Induce apoptosis in virally infection and tumour cells
- Expresses CD8
- Also expresses CD3, TCR
- Mediates acute and chronic organ rejection
What are the functions and properties of B cells?
- Major cell of humoral immune response
- Acts as an antigen presenting cell
- Mediates hyperacute organ rejection
What are the functions and properties of plasma cells?
- Differentiated from B cells
- Produces large amounts of antibody specific to a particular antigen
What is the function of T lymphocytes?
- T lymphocytes increase apoptosis to destroy cells that have been hijacked by viruses and pathogens
What is the function of B lymphocytes?
- B cells release antibodies used to attack invading pathogens
What are the 2 primary lymphoid organs?
Bone marrow
Thymus
Define secondary lymphoid organs?
Organs where lymphoid cells fight microbes
