Introduction to the immune system Flashcards
1
Q
What is Immunology?
A
Immunology is the study of our body’s sytems for preventing and treating diseases.
2
Q
How is the immune system organised?
A
- The Immune System is split into a frontline defence (Innate Immunity) and a second, more specific defence (Adaptive Immunity).
- The adaptive immunity can be humoural (ie. B cells and antibodies) or it can be cellular (ie. T cells).
- White Blood Cells (WBCs) are key players in the immune system.
3
Q
Briefly, describe the innate immune system.
A
- The innate immune system is your ever-present defence against infection.
- It is made up of barriers that keep viruses, bacteria, parasites and other foreign particles out of your body or limit their ability to spread and move throughout the body.
- Innate immune responses are rapid and independent of antigen.
- The importance of innate immunity is demonstrated by the fact that you are normally healthy despite the barrage of potential infectious challenges that you face every minute.
4
Q
What does the innate immune system include?
A
- EPITHELIAL BARRIERS to the environment (eg. skin, gastrointestinal tract, respiratory tract) that prevent microbe entry.
- SECRETIONS at mucosal surfaces - flushing action and antimicrobial properties.
- CELLS that are resident in tissues (eg. mast cells) or circulating in the body (eg. neutrophils).
- Circulating PROTEINS in the blood (eg. complement proteins).
- CYTOKINES (eg. interferons) that are locally produced by infected cells
5
Q
What are the main functions of innate immunity?
A
- Prevention, control and elimination of infection.
- Removal of damaged cells and initiation of tissue repair.
- Activate the adaptive immune response.
- Influence the type of adaptive response that will develop.
6
Q
What are some important features of the innate immune system?
A
- It’s the first line of defence in preventing infection.
- It responds to microbes and products of injured cells.
- It has non-specific activity.
- It has no “memory”, so if the challenge is repeated, the innate immune response will be the same.
7
Q
Why is our innate immune system required?
A
- We would not be able to survive on our adaptive immune system alone.
- The adaptive immune system takes a few days to really kick in, while the innate immune system provides immediate and early protection.
8
Q
What is phagocytosis and why is it important?
A
- Phagocytosis is a process by which cells internalise solid matter, including microbial pathogens.
- This is a vital part of the innate immune response to pathogens, and plays an essential role in initiating the adaptive immune system.
9
Q
What are the ‘professional’ phagocytes?
A
- Most cells are capable of phagocytosis, but it is the professional phagocytes of the immune system that truly excel at this process.
- These cells include NEUTROPHILS, MACROPHAGES and DENDRITIC CELLS.
- In these cells, phagocytosis is a mechanism by which microorganisms can be contained, killed and processed for antigen presentation.
10
Q
How do immune cells know when to get to work?
A
- The immune system detects ‘danger’ through a series of pathogen-associated molecular patterns (PAMPs) or damage-associated molecular pattern molecules (DAMPs) working in concert with both positive and negative signals derived from other tissues.
- PAMPs are small molecular motifs censerved wiyhin a class of microbes. A vast array include glycans, lipopolysaccharides, bacterial flagellin, lipoteichoic acid, peptidoglycan and nucleic acid variants normally associated with viruses such as double-stranded RNA.
- DAMPs are molecules released by stressed cells undergoing necrosis. Some are proteins - heat-shock proteins and cytokines. Non-protein DAMPs include ATP, heparin sulfate, and DNA.
- PAMPs and DAMPs are recognised by Pattern Recognition Receptors (PRRs) on immune cells.
11
Q
Describe dendritic cells.
A
- Dendritic cells are widely distributed in lymphoid tissues, mucosal epithelium and body organs.
- They are important in phagocytosis (as they are phagocytes).
- This is because their main function is to process antigen material and present it on the cell surface to the T cells of the immune system.
- They act as messengers between the innate and the adaptive immune systems.
12
Q
What is inflammation?
A
- Inflammation is the process whereby the immune cells (which are normally distributed throughout the body) can be recruited and concentrated to a site of infection or damage.
13
Q
How does inflammation occur and what are the main events in inflammation?
A
- Following PAMP or DAMP recognition, PRRs trigger proinflammatory and antimicrobial responses by inducing the release of a broad range of cytokines.
The main events in inflammation are:-
- Increased blood supply to the affected area.
- Increased permeability of the vasculature.
- Migration of WBCs out of the blood capillaries into the affected tissue.
14
Q
Briefly, describe the adaptive immune system.
A
- The adaptive immune system is the second line of defence and responds to infection.
- It takes day-weeks to develop the immune response, but it is also: -
- potent
- responsive to any potential foreign entry
- highly specific
- has ‘memory’
The importance of adaptive immunity is that it provides a powerful defence against infection if the innate immune system is breached.
15
Q
What are the main (cellular) components of the adaptive immune system?
A
The main components of the adaptive immune system are:-
- DENDRITIC CELLS - they capture, process and present antigens.
- T-LYMPHOCYTES - they control the immune response by releasing interleukins to activate B lymphocytes and macrophages (T helper cells), and directly kill off infected or tumour cells (cytotoxic T cells / T killer cells).
- CYTOKINES - they’re soluble proteins secreted mainly by T cells that control activities of other cells.
- B LYMPHOCYTES - they produce and secrete antibodies, which are proteins that specifically bind target molecules (antigens) on microbes or cells.
16
Q
What is the Lymphoid System?
A
- Immunological cells are largely organised (not randomly) into tissues and organs for best efficiency.
- This is an advantage as it protects key areas of the body.
- Collectively, these structures are known as the lymphoid system.
17
Q
Define primary and secondary lymphoid organs.
A
- PRIMARY LYMPHOID ORGANS -
- They are sites of maturation of white blood cells.
- The WBCs differentiate from stem cells, multiply, are programmed and mature into functional cells.
- SECONDARY LYMPHOID ORGANS -
- They provide the site of interaction between antigens and WBCs.
- They also allow the spread of the immune response.
- Secondary lymphoid organs are associated with systemic and mucosal immune compartments (blue).
18
Q
Describe the Lymphatic System.
A
- The lymphatic system is part of the circulatory system and an important part of the immune system.
- It comprises a network of lymphatic vessels that carry lymph fluid and cells from the tissues back into the blood stream.
19
Q
Describe lymph nodes.
A
- At regular intervals along the lymph vessels are organised structures called lymph nodes.
- Major areas with a lot of lymph nodes are the neck, armpits and groin.
- The lymph arrives at the node by an afferent lymphatic vessel, filters through multiple layers if antigen presenting cells, T cells and B cells, then finally exits via the efferent lymphatic vessel.
- The dense concentration of immune cells provides an ideal environment for initiating immune responses and communication between immune cells.
- Lymph nodes are common battleground sites for the immune system and infections.
20
Q
What is the hallmark of adaptive immunity? List, and describe, the two types of molecules involved in this process.
A
- The hallmark of adaptive immunity is the ability to specifically recognise foreign antigens.
- The two molecules involved in this process are :-
- Immunoglobulins (Igs)
- T cell antigen receptors (TCRs).
IMMUNOGLOBULINS:
- Immunoglobulins (antibodies) are glycoproteins produced by plasma cells.
- They specifically recognise and bind strongly to particular antigens on pathogens, and prevent disease or aid in the destruction of the pathogen.
- There are different classes and subclasses of immunoglobulins, which differ in their structure, biological features and distribution.
- Immunoglobulins are produced by B cells, so they are a part of humoural immunity.
T CELL ANTIGEN RECEPTORS (TCRs):
- T cell receptors are found on the surface of T cells.
- They are responsible for recognising processed fragments of antigens (peptides) which are ‘presented’ by host cells.
- The binding between the TCR and antigen peptides is relatively weak compared to antibodies.
- When the TCR engages with the antigen peptide, the T lymphocyte is activated through a series of biochemical events (signal transduction), leading to cell proliferation and biological activity (eg. cytokine production).
- TCRs are produced by T cells, so they are a part of cellular immunity.
21
Q
What are B cells?
A
- B cells are lymphocytes which, when activated, become plasma cells and then produce antibodies.
- This is often known as humoural immunity.
22
Q
Describe the structure and function of antibodies.
A
- Antibodies are glycoproteins that are made by B cells and plasma cells.
- They bind specifically and with high affinity to ‘non-self’ antigens.
- Antigens are usually proteins or carbohydrates attached to, or secreted by, microbes and infected cells.
- Antibodies can neutralise targets, or recruit other components of the immune system to kill targets.
- Once bound to a cell or bacterium, antibodies can recruit other components of the immune system to kill targets by Fc-mediated effector functions.
- These include white blood cells (eg. macrophages, dendritic cells).
- It activates the complement cascade.
- The antibody Fc also binds to the neonatal Fc receptor.
23
Q
Describe the structure and function of T cells.
A
- T cells control the immune response and combat microbes that are inside cells (intracellular).
- Different T cells have different functions and are distinguished by the array of proteins on the cell surface (Cluster of Differentiation (CD) markers).
- Two major groups are CD4 (helper T cells) and CD8 (cytotoxic T cells).
- Depending on how the antigen is presented, different T cells are engaged, leading to different T cell responses.
