Topic 20: Immune System Flashcards
What is the immune system and how does it express immune responses to perform functions?
Immune system is a collection of cells, tissues, and molecules that mediate resistance to infections and eliminate tumours.
It displays coordinated and tightly controlled reactions to infectious microbes which is known as immune response.
The immune responses help to prevent infections, eradicate established infections, detect and eliminate tumours, and tolerate self.
What is the overall role of immunity?
Immunity displays resistance against infectious diseases caused by bacteria, virus, fungi, parasites, and tumour.
Besides killing microbes, immunity involves a wider set of functions to keep our body in good working order.
Identify and describe different types of immune deficiencies
- Congenital (primary) immune deficiencies: inherited traits leading to complete lack of key cells or molecules of immune system
- Acquired (secondary) immune deficiencies: caused by diseases or other factors (malnutrition, HIV, etc.)
Identify the locations of immune system and immune cells/molecules
- Immune system in integrated with all other systems (GI, nervous, cardiovascular, respiratory, skin, endocrine)
- Immune cells are scattered all around the body. Some travel or migrate all around while some stay in 1 place, resident immune cells.
In what ways do immune molecules work?
Molecules act in
- Autocrine manner (effect on itself)
- Paracrine manner (effect on surrounding cells)
- Endocrine manner (effect on other cells in distance)
Describe how immune cells play a role of physical and chemical barriers in our body
Immune cells together create:
- Epithelial cells (skin, gut, GI tract)
- Secretions (sweat, wax, tears)
- Mucus in nose, trachea, gut
- Urine
- Proteolytic enzymes
- Low stomach pH
- Normal gut flora
How do immune cells and molecules access other systems?
Via blood and lymphatic vessels
Identify and describe organs and tissues that are important to the synthesis and accumulation of immune cells
Bone marrow had stem cells which then become myeloid progenitor, producing cells in innate immune system, and lymphoid progenitor, producing lymmphocytes in adaptive immune system.
- Central sites: refer to lymphoid tissues or organs
+ Primary: bone marrow and thymus
+ Secondary: spleen, lymph nodes, mucosal and cutaneous associated with lymphoid tissues (accumulation of immune cells) - Peripheral sites: all other tissues and systems
Describe hallmarks of the innate immune system
- Early and rapid
- Short-lived
- Repetitive
- Interactive with others in IIS and cells in AIS
- Non-reactive to the host
How do immune cells differentiate between self and non-self cells?
Different microbes express different “patterns” that are not detected in our own cells.
Epithelial, endothelial, and resident immune cells have receptors to sense those “patterns”
==> recognize and sense the differences/danger
Identify and describe components of the innate immune system
- Epithelial cells
- Cells present in circulation and tissues:
+ Phagocytes (like neutrophils and macrophages): ingest microbes
+ Exocytes (like eosinophils, mast cell, basophils): release active mediators from granules in the cytoplasm into ECF to kill microbes - Molecules: cytokines and blood proteins
What are cytokines and what are their functions?
Cytokines are proteins produced by different cell types.
Cytokines are responsible for modulating inflammatory and immune responses/activity. They are also principal mediators of communication between cells.
Target cells in autocrine, paracrine, and endocrine manner
Describe tissue resident mast cells
- Mast cells reside in peripheral tissues exposed to the environment (skin, lung, gut)
- Have receptors, and already reside in tissues, no need to recruited from blood –> 1st responders
- Have antibacterial functions by secreting granules of histamine, cytokines, and other soluable factors into ECF
–> increase vascular permeability
–> increase inflammation reaction
Describe the hallmarks and components of adaptive immune system
- Adapts to microbial invaders
- Consists of lymphocytes and its products (antibodies)
+ Lymphocytes have receptors on surface to recognize a wide range of antigens - Differentiation and expansion of lymphocytes into:
+ Effector cells (kill)
+ Memory cells (remeber to respond on 2nd encounter - Use cells and molecules of IIS to eliminate microbes
Describe the process conducted by the immune system when danger is detected
- The intrusion of microbes into tissues and the destruction of cells trigger immune responses. (cellular debris produced from cell necrosis ← physical, biological, chemical insult)
- Mast cells are the first to respond which release granules of histamine.
- Histamine then increases vasodilation and permeability of blood vessels.
- Plasma proteins like complement and antibodies are released from blood vessels into tissues which neutralize the pathogens.
- Macrophages then start to ingest microbes to destroy them.
- Cytokines are released by macrophages which increase the expression of adhesion molecules on the walls of blood vessels for white blood cells.
- Neutrophils present in the blood vessels adhere to the vessel’s walls.
- They then roll along the vessel’s walls (endothelium), ready to be extravasated.
- Neutrophils are squeezed out of the blood vessels into the tissues. They follow the chemokines gradient (low to high concentration at the source of inflammation) to the site of infection.
- They also ingest and eliminate microbes. (phagocytose foreign substances and cell debris, while secreting inflammatory cytokines to further intensity the inflammation)
Describe how phagocytosis occurs and how microbes are killed
- Maccrophages and neutrophils injest microbes by phagocytosis
- Microbes bind to receptors of phagocytes
- Extension of phagocyte plasma membrane around the particle
- The membrane then closes up and pinches off and the microbe is enclosed in a membrane-bounded vesicle, called phagosome.
- Phagosomes fuse with lysosomes to form phagolysosomes.
- Enzymes and toxic substances in phagosomes kill microbes
How do immune cells detect and migrate to the source of infection/inflammation?
- Sources of infection/inflammation release different chemokines which disperse in gradient.
- Different cells have different chemokine receptors
- Detect and follow the chemokines flow to the source of infection
How do immune cells are squeezed out of the blood vessels?
Leukocytes, for example, will roll along the blood vessels walls where infection/inflammation occurs and adhere tightly to the walls. Then, they are extravasated or squeezed out of vessels’ walls into tissues without disrupting the membrane. FInally, they follow the chemokines gradient to the source of infection and inflammation.
Is flammation good or bad?
- A little bit of inflammation is good because it gets the immune system going.
- Too much inflammation may cause widespread infection and septic shock. If chronic can lead to severe diseases and even motality.
Describe 2 main types of Lymphocytes
- B lymphocytes (B cells): discovered in “bursar of Fabricius”
- T lymphocytes (T cells): matured in the thymus (where T cells are matured to not react to host/not kill self-cells)
Describes types of adaptive immunity
- Hummoral immunity: involved B lymphocytes
+ B cells have receptors that can sense extracellular microbes
+ These receptors are then released as antibodies specifically targeting that kind of microbes
+ The antibodies then bind to microbes to eliminate them and prevent infections - Cell-mediated immunity: involved helper T cells and killer T cells
+ Helper T cells:
~ Have receptors that can sense phagocytes which have phagocytose microbes
~ Release cytokines to help the phagocytes digest microbes
–> elimination of phagocytosed microbes
+ Cytotoxic T cells:
~ Have receptors that can sense intracellular microbes that have infected and multiplied in cells
~ Bind to infected cells to
–> kill infected cells and eliminate reservoirs of infection
Identify and describe 2 types of T lymphocytes
- Helper T cells (Th cells):
+ Help other cells in immune responses
eg. help B cells to produce antibodies, help T cells to be “good” T cells (regulate its activity, not kill self), help macrophages to digest phagocytosed microbes
+ Some regulate/suppress rather than activate immune responses ==> regulatory T cells - Cytotoxic T lymphocytes (CTLs):
+ Kill target cells in a highly specific way
+ Get help from Th cells
+ Functions: fight back viral infections and create anti-tumour immunity
Describe different types of immunological tolerance and the risks associated with this systen breaking down
Immunological Tolerance is the system determining which lymphocytes clones are allowed to survive.
- Central: occurs in primary lymphoid tissues (bone marrow for B cells and thymus for T cells)
- Peripheral: mediated primarily by regulatory cells
If this system breaks down, the person is more susceptible to autoimmune diseases
Describe how genes and environment affect autoimmune diseases
- Many genes inherited are responsible for T-cells activation and maintain immunological tolerance by finding/destroying self-reactive lymphocytes and controling activity of regulatory cells.
+ if these genes are missing or mutated, higher risks for autoimmune diseases - Environment:
+ AD are often preceded by infections
+ More prevalent in women
+ Local trauma may trigger inflammatory reasponses revealing hidden antigens to which immune system responses.
