Immunology Lecture 26+27 Flashcards
Learning objectives
Aims
To provide an introduction into the basic concepts of immunology and provide an
overview of how dysfunction of the immune system can lead to disease and
conversely how understanding immunology has revolutionised modern medicine
Learning Objectives
● Understand the difference between innate, adaptive and passive immunity
● Describe the roles of B and T cells
● Describe the role of the different components of the immune system
● Understand how dysfunction of the immune system can lead to disease
● Understand how understanding immunology has revolutionised modern
medicine.
Define immunity
The state of being insusceptible or resistant to a noxious agent or process, especially a pathogen or infectious disease
List some examples of first line defences (6 points)
● Skin
● Tears
● Cilia and mucus
● Stomach acid
● Urine flow
● Friendly bacteria
How does skin act as a first line of defence against pathogens?
Acts as physical barrier
How do tears act as first line of defence
Tears contain lysozyme enzymes which can break down bacterial cell walls
How do cilia and mucus act as a first line of defence?
Mucus can trap bacteria/fungi/pathogens. Cilia actively beat which moves the mucus lining our bronchioles up into the throat, where the mucus is swallowed and any pathogens in the mucus are killed by acids in the stomach
How does the stomach act as a first line of defence?
Low pH, contains hydrochloric acid which can kill pathogens. Proteases e.g. pepsin can be activated in the stomach, killing pathogens
How does urine flow act as a first line of defence?
●urine flow helps flush out pathogens from the urinary tract
How do ‘friendly bacteria’ form a first line of defence?
●Friendly bacteria e.g. those on our skin or in our stomach are naturally occurring and form a microbiome which acts as competition to reduce ability of pathogens to colonise and grow
Which type of immunity is classed as first line of defence?
Innate Immunity
What is the function of innate immunity?
innate immunity provides a quick and nonspecific defense against a variety of pathogens, creating barriers, using cellular components, and initiating inflammatory responses to prevent or limit infections
Compare and contrast innate immunity, adaptive immunity and passive immunity.
(Specificity, Timing, Memory, Components)
Specificity:
● Innate immunity is nonspecific.
●Adaptive immunity is highly specific.
●Passive immunity can be specific if it involves the transfer of antibodies with defined specificities.
Timing:
●Innate immunity provides immediate, rapid defense.
●Adaptive immunity has a delayed response.
●Passive immunity provides immediate but temporary protection.
Memory:
●Innate immunity lacks memory.
●Adaptive immunity has immunological memory.
●Passive immunity does not confer memory.
Components:
●Innate immunity involves physical barriers, phagocytes, and the complement system.
●Adaptive immunity involves B cells, T cells, antibodies, and memory cells.
●Passive immunity involves the transfer of antibodies.
What are the 2 main types of hematopoietic cells?
Which immunity is each one involved in?
Myeloid cells - innate immunity
lymphoid cells - adaptive immunity
What are PAMPs
Molecules associated with pathogen infection that act as ligands for Toll-like Receptors/ TLRs.
TLRs detect infection and initiate the immune response
What is the function of TLRs?
Where can they be found/expressed?
What does it mean when you said TLRs are expressed somewhere?
Function - detection of infections and the initiation of mainly the innate immune response but also influence adaptive immune response
Expressed - expressed on the surface of various immune cells e.g. B cells dendritic cells, macrophages and neutrophils (all myeloid cells)
Means that is where they can be found. Expressed on neutrophils, dendritic cells and macrophages = you will find TLRs on the outer membranes of these cells
What are some of the main myeloid (involved in innate immunity) cells?
Dendritic cells
neutrophils
macrophages
What is the purpose of TLRs in innate immunity?
TLRs have recognition sites on their extracellular domains which bind DAMPs and PAMPs.
TLRs know something has bound to them via internal signalling pathway that ultimately changes cell behaviour and gene expression for pro inflammatory cells
What myeloid cells are TLRs expressed by / found on the outer membrane of?
Dendritic cells, neutrophils, macrophages
In innate immunity, what happens when cells recognise PAMPs? What are some of the outcomes?
When cells involved in innate immunity (such as dendritic cells, macrophages and neutrophils) recognise PAMPs, they are activated. The cells then secrete ligands which attract additional cells involved in innate immunity
After this, the inflammatory response can be triggered as well as
- Further release of pro-inflammatory cytokines
- Fever, which inhibits pathogen proliferation
What are the 3 main specialist phagocytic cells recruited in innate immunity?
State some details about them.
(macrophages, neutrophils, eosinophils)
Neutrophils - short lived, abundant in blood but not in tissue, respond and migrate to sites of infection
Macrophages - long lived, abundant in areas likely to be exposed to pathogens e.g. lungs and gut
Eosinophils - specialists in attacking objects too large to engulf
What are some of the functions of dendritic cells? 3 points
- express large variety of recognition receptors e.g. TLRs
- phagocytoses pathogens
- migrate to lymphoid tissues and activate and stimulate T-cells of the adaptive immune system
What type of cells are involved in adaptive immunity?
Lymphocytes
What is needed to activate T cells?
APCs, usually dendritic cells.
dendritic cells have a role in phagocytosis, antigen capture, antigen processing, antigen presentation
What are the 2 main types of lymphocytes?
B - Cells mature in bone marrow
T - Cells mature in Thymus
chatgpt What are B cells and T cells?
what are they
function
memory
location
B cells + T cells are two major types of lymphocytes, a type of white blood cell crucial for the immune system. Both B cells and T cells play key roles in adaptive immunity, providing specific and long-lasting protection against pathogens.
Function:
B Cells:
- primarily responsible for antibody-mediated immunity
-produce antibodies that can recognize and neutralize pathogens
- can differentiate into plasma cells
T Cells:
- involved in cell-mediated immunity, involving direct cellular responses against infected or abnormal cells.
- T cells can directly kill infected cells or regulate immune responses
- T cells recognize antigens presented on the surface of other cells.
- Helper T cells recognize antigens on the surface of APCs,
- cytotoxic T cells directly recognize antigens on infected cells
Memory:
B Cells:
- B cells generate memory B cells during an immune response. Memory B cells “remember” the specific antigens encountered, allowing for a faster and more effective response upon subsequent exposure to the same pathogen.
T cells:
- T cells generate memory T cells during an immune response. Memory T cells contribute to the long-term immune memory allowing for a faster and more effective response upon subsequent exposure to the same pathogen
Location:
B cells mature in bone marrow
T cells mature in the thymus
What is the name for the first branch of lymphocyte from the common lymphoid progenitor? What is their function?
(Natural killer cells are part of innate immunity)
Natural Killer Cells
Function - Participate in early defence against foreign cells and autologous cells undergoing stress e.g. microbial infection or tumour transformation
What are the 3 subtypes of T-cells?
Cytotoxic t-cells = kill infected host cells
Helper t-cells - activate macrophages, dendritic cells, b cells and cytotoxic t-cells by secreting cytokines and displaying co-stimulatory proteins on their surface
Regulatory t-cells = inhibit other t-cells
how does adaptive immunity work? (6 points)
Body randomly generates a collection of lymphocytes, most of which are dormant
- When an antigen is presented (e.g. by dendritic cells or t-helper cells) to dormant lymphocytes, those with binding affinity to the antigen activate - Binding of antigen to activated lymphocytes leads to proliferation and clonal expansion Expansion triggers differentiation into effector cells - An expansion round occurs every time an antigen is encountered - Subsequent encounters stimulate memory cells made from previous encounter - this time a bigger pool of cells will be able to bind
Body can respond to multiple antigens at once
Give 3 examples of modern medicines created through the understanding of immunology.
Cancer vaccines - direct immune response designed to prevent specific cancer epitopes and cancer causing pathogens
oncolytic viruses - lab modified viruses that can infect and kill certain tumour cells
CAR T-cell therapy:
- Take T-cells from PT and infect them with recombinant virus that causes expression of a TCR with an antigen binding domain specific to a tumour antigen
- This generates T-cells able to attach to specific tumour cells, which are transfused back into the PT
Give an example of a disease caused by dysfunction in the immune system (HIV)
- virus which infects T-helper cells, dendritic cells and macrophages expressing CD4 receptor
- infected immune cells no longer function and trigger t-helper cells to target cells required for adaptive immunity
- results in immune deficiency leading to infections and cancers not normally seen in those with healthy immune systems
