Cells: Infection And Immue System Response Flashcards
What is an antigen?
Antibody generating molecule recognized as Non-self or foreign
Antigens can stimulate an immune response.
What are examples of antigens?
- Proteins
- Polysaccharides
- Glycoproteins
- Glycolipids
- Free molecules (e.g., toxins)
Antigens can be found on microorganisms, viruses, tissue or organ transplants, and as free molecules.
Where can antigens be found?
- Cell surface of a microorganism
- Surface of a virus
- Cell surface of a tissue or organ transplant
- As a free molecule (e.g., toxin)
Antigens are typically foreign substances that stimulate an immune response.
What characterizes the most effective antigens?
They are large and complex
The complexity and size help in eliciting a stronger immune response.
What is antigen variability?
Changes in the shape of an antigen due to mutations in the pathogenic DNA
This can render previous immunity ineffective.
How does antigen variability affect immunity?
Previous immunity becomes ineffective if the shape of the antigen changes
Memory cells in the blood will only recognize the old antigen shape.
Why is a new flu vaccine created each year?
The influenza virus mutates and changes its antigens quickly
This rapid change necessitates updated vaccines to match the new antigen shapes.
True or False: Antigens are always foreign substances.
False
While they are usually foreign, not all antigens are.
Fill in the blank: Antigens can be found on the _____ of a virus.
surface
This is one of the locations where antigens are commonly found.
What are the two types of defence mechanisms?
Non-specific and Specific
Non-specific defense
Response is immediate and the same for all pathogens: it is a physical barrier e.g skin, or phagocytosis
Specific defense mechanism
Response is slower and specific to each pathogen. It is a cell mediated response e.g T lymphocytes, or a humoral response e.g B lymphocytes
Cytokines
Cell signalling molecules that aid cell-to-cell communication in immune responses and stimulate the movement of cells towards sites of inflammation, infection and trauma
What generally triggers inflammation?
Occurs when an infection is relatively localised
What type of cells release histamines during inflammation?
Mast cells
Where are mast cells typically found?
In connective tissue below the skin and around blood vessels
What effect do histamines have on blood vessels?
Cause blood vessels to dilate, leading to local heat and redness
What happens to capillary walls during inflammation?
Become more leaky, allowing fluid and white blood cells to exit
What type of white blood cells are mainly forced out of capillaries during inflammation?
Neutrophils
Fill in the blank: Histamines cause blood vessels in the area, particularly ________, to dilate.
arterioles
What are the main components of the fluid that leaks out of capillaries during inflammation?
Plasma, containing WBCs and antibodies
True or False: Basophils are responsible for releasing histamines during inflammation.
False
What are the common symptoms associated with inflammation?
Swelling and pain
What are non-self cells or molecules?
Cells or molecules that the immune system has not had exposure to during maturation or does not normally encounter in the body
Non-self cells trigger an immune response to destroy them.
What happens if a non-self cell is detected?
A response will be triggered to destroy the cell
This is a key function of the immune system.
What type of entities can the immune system identify?
The immune system can identify:
* Pathogens (e.g., bacteria, fungi, viruses)
* Cells from other organisms of the same species
* Abnormal body cells (e.g., cancer cells)
* Toxins released by pathogens
These identifications are crucial for the immune response.
Fill in the blank: The immune system can identify pathogens such as _______.
[bacteria, fungi, viruses]
Examples include HIV as a virus.
True or False: The immune system can identify cells from other organisms of the same species.
True
This is particularly relevant in organ transplants.
What are some examples of abnormal body cells identified by the immune system?
Abnormal body cells include cancer cells
The immune response can target these cells for destruction.
What kind of toxins can the immune system identify?
Toxins released by pathogens
An example is cholera toxin.
What are Neutrophils?
A type of phagocyte that is located in the blood and breaks down the pathogen by phagocytosis
What is a Macrophage?
A type of phagocyte located in the lymph nodes that carries out phagocytosis to break down pathogens
Phagocytosis definition
The cellular process of engulfing solid particles using the cell membrane - carried out by phagocytes
Endocytosis
Infolding of the membrane to create an internal vesicle. Receptors on the phagocyte will recognise non-human cells and begin to engulf them
Process of Phagocytosis
- Phagocytes are in the blood and tissues and any chemicals or debris released by pathogens or abnormal cells attract the phagocytes and they will move towards these cells
- There are many receptor binding points on the surface of phagocytes. They will attach to the chemicals or antigens on the pathogen via these receptors
- The phagocyte changes shape to move around and engulf the pathogen
- Once engulfed, the pathogen is contained within a phagosome vesicle
- A lysosome within the phagocyte will fuse with the phagosome forming a phagolysosome and release its contents
- The lysozyme is released into the phagosome. This is a lytic enzyme which hydrolyses the pathogen
- The pathogen is destroyed
- The soluble products are absorbed and used by the phagocyte and the insoluble products are removed from the cell by exocytosis
Types of phagocytes
Neutrophils, Macrophages, Dendritic cells, B-Lymphocytes
Cell mediated immunity
A specific immune response that utilises T-cells to target own-body cells and antigen presenting cells. T cells respond to antigens presented on the surface of our own cells
Humoral immunity
A specific immune response involving B-lymphocytes and antibodies. Some of these B-lymphocytes become plasma cells that secrete lots of antibody molecules (specific to the antigen) into the blood, lymph or linings of the lungs and the gut. B cells respond to free antigens found in our blood plasma and tissue fluid
T lymphocyte production
Developed from stem cells in the bone marrow and mature in the thymus
B lymphocyte production
Developed from stem cells in bone marrow, lymphatic tissue, spleen and lymph nodes and mature in the bone marrow
Antigen Presenting Cells (APCs) definition
Any cell that presents a non-self antigen on their surface
APC examples
- Infected body cells will present the viral antigens on their surface
- A macrophage which has engulfed and destroyed a pathogen will present the antigen on their surface
- Cells of a transplanted organ will have different shaped antigens on their surface compared to your self-cell antigens
- Cancer cells will have abnormal shaped self-cell antigens
Types of T lymphocyte
- Cytotoxic T cell (Killer T Cell)
- Helper T Cell (Stimulates the division of B cells)
What is the role of T cells in a cell mediated response?
Once the T cells response has been activated / become competent, because the complementary antigen on the APC has been presented and binds to its receptors, it then divides by mitosis to produce large quantities of itself. These clone T Helper cells will:
- Stimulate B cells to divide
- Stimulate phagocytes to engulf the pathogens
- Activate Cytotoxic T cells which go on to kill infected body cells
- Develop into memory cells
Cytotoxic T cell function and usage
- Destroy abnormal or infected cells via the release of the protein perforin, which embeds in the cell surface membrane and creates a pore so that any substance can enter or leave the cell, causing cell death
- Most commonly, cell death of this kind occurs in viral infections as viruses infect body cells. These cells are sacrificed to prevent cell replication
Cell mediated immune response pathway
- Various cells, mainly phagocytes, take up the pathogens antigen and present on their surface (APCs)
- Specific T cells (T helpers) have receptors that fit exactly onto these antigens
- Activated T.h cells multiply by mitosis, producing a large number of cloned cells which have differing functions
- The T.h cells activate B cells and thus, humoral immunity
- Cytotoxic T cells attach to infected or pathogenic cells and release perforin, causing cell death
Why is the T cell response described as ‘cell-mediated?’
T cell response is described as cell mediated because T cells only respond to antigens which are present on own body cells and not antigens detached from the cells and within body fluids such as the blood: it is an immunity involving body cells
Lymphocytes
Lymphocytes are white blood cells involved in the specific immune response. All lymphocytes are made in the bone marrow (B cells also mature in the bone marrow.)
Humoral response
The response involving B cells and antibodies. Antibodies are soluble and are transported in body fluids. The term ‘humor’ derives from an old term for body fluids, hence the name ‘humoral response.’
B cell activation process
- Antigens in the blood collide with their complementary antibody on a B cell
- The B cell takes in the antigen by endocytosis and then presents it on its cell surface membrane
- When this B cell collides with a helper T cell receptor, the B cell is activated to go through clonal expansion and differentiation (a.k.a clonal selection)
- B cells undergo mitosis, making large numbers of cells which differentiate into plasma cells or B memory cells
- The plasma cells will make antibodies, whilst the B memory cells will divide rapidly into plasma cells when re-infected with the same pathogen (this is done to produce large quantities of antibodies rapidly)
There are approximately 10 million different B cells, each with specific antibodies on their surface complementary to 10 million different antigens
Memory B cells functions and characteristics
- Memory B cells can live for decades in your body, unlike plasma cells, which are short-lived
- Memory B cells do not make antibodies, rather they will divide by mitosis and make plasma cells rapidly if they collide with an antigen they have previously encountered
- This results in large numbers of antibodies being produced so rapidly that the pathogen is destroyed before any symptoms can occur
- Memory B cells are an example of active immunity
Antibodies functions and characteristics
- Antibodies are quaternary structure proteins made up of four polypeptide chains
- Each different antibody has a different shaped binding site, which is the variable region. The shape of the antigen-binding site is unique to the shape of a particular antigen
Agglutination
Antibodies are flexible and can bind to multiple antigens to clump them together. This process is called agglutination: it is carried out to make it easier for phagocytes to locate and destroy the pathogens
Humoral immunity: the primary response
- The initial, immediate response to an antigen, producing antibodies and memory cells
- Plasma cells secrete antibodies into the blood plasma. Each cell can make approximately 2000 antibodies per second, but the cell only survives a few days
- The primary response produces a lesser concentration of antibodies than a secondary immune response
Humoral immunity: the secondary response
- The response in which the infection is seen for a second time and is initiated by memory cells
- Memory cells circulate in the blood and tissue fluid, surviving for decades. When they encounter the same antigen at a a later date, they divide rapidly and develop into plasma cells and more memory cells
- A larger response is seen with a reduced amount of the antigen: It’s more rapid so that the pathogen can be destroyed before it fully infects the body - long term immunity
Active immunity
Immunity created by your own immune system following exposure to the pathogen or its antigen. It can be either active natural or active artificial
Active natural immunity
Following infection and the creation of the body’s own antibodies and memory cells
Active artificial immunity
Following the introduction of a weakened version of the pathogen or antigens via a vaccine
Passive immunity
A type of immunity that can be active or passive
Passive artificial immunity
Antibodies are introduced into the body. The pathogen doesn’t enter the body, so plasma cells and memory cells are not made. E.g. if you get cut on metal, you have to get a tetanus shot, which is a suspension of antibodies specific to tetanus.
Passive natural immunity
E.g antibodies passed to a foetus through the placenta or the breast milk. This does not provide long term immunity
Vaccines
Small amounts of weakened or dead pathogen/antigens are introduced into the mouth or by injection. Exposure to the antigen activates the B cell to go through clonal expansion and differentiation. Memory B cells can act as a booster dose
Herd immunity
If enough of the population are vaccinated the pathogen cannot spread easily amongst the population. This provides protection for those who are not vaccinated e.g those who are already too ill to have a vaccine or have lowered immunity or are too young
Human immunodeficiency virus (HIV)
- A virus that affects the human immune system
- It eventually leads to acquired immunodeficiency syndrome (AIDs)
- AIDs is a condition where the immune system deteriorates and eventually fails
- This makes a person more vulnerable to other infections like pneumonia
HIV structural aspects
- Core: stores genetic material (RNA) and the enzyme reverse transcriptase which are needed for viral replication
- Capsid: outer protein coat
- Envelope: extra outer layer, made out of membrane taken from the host’s cell membrane
- Protein attachments: on the exterior of the envelope to enable the virus to attach to the host’s helper T cell via CD4
HIV Replication pathway
- HIV is transported around in the blood until it attaches to a CD4 protein on the helper T cells
- The HIV protein capsid then fuses with the helper T cell membrane, enabling the RNA and enzymes from HIV to enter
- The HIV enzyme reverse transcriptase copies the viral RNA into a DNA copy and moves to the helper T cell nucleus. This is why it is called a retrovirus
- Here mRNA is transcribed, and the helper T cell starts to create viral proteins to make new viral particles
Monoclonal antibodies
Many of the same type of antibody formed from one B Plasma cell. Therefore, the antibodies are all the same and are specific to one binding site on one protein antigen and so are able to target specific chemicals/body cells
Direct monoclonal antibody therapy
- Some cancers can be treated using MABs
-This works by attaching MABs with complementary binding sites to the antigens on the outside of cancer cells - While the antibodies are bound to the cancer antigens this prevents chemicals binding to the cancer cells which enable uncontrolled cell division
- They are specifically designed to bind only to cancer cells
Indirect monoclonal antibody therapy
- Cancer can also be treated with monoclonal antibodies complementary in shape to the antigens on the outside of cancer cells which have drugs attached to them
- These cancer drugs are delivered straight to the cancer cells and kills them, reducing the harmful side effects of traditional chemotherapy
- This is often referred to as ‘bullet drugs’
Monoclonal antibodies can be used for…
- Pregnancy
- Influenza
- Hepatitis
- Chlamydia
- Prostate Cancer
Enzyme-Linked Immunosorbent Assay (Quantitative and Indirect) process
- Apply sample containing antigen to well
- Wash well several times to remove any excess
- Add on antibody specific for the antigen
- Allow antibody molecules to stick to antigens
- Wash again to remove any excess antibodies
- Introduce a second antibody which is specifically designed to bind to the first antibody and has an enzyme attached
- Wash again to remove any unbound second antibody
- Add substrate (colourless)
- Intensity of colour can be used to determine amount of antigen
ELISA Test (Indirect) summarised process
- Antigen
- Wash
- Antibody 1
- Wash
- Antibody 2 + enzyme
- Wash
- Substrate
- Result
ELISA (direct) process (summarised)
- Antibody on well surface
- Wash
- Add sample (antigen)
- Wash
- Antibody with enzyme
- Wash
- Substrate
- Result
