Immunology Flashcards
What is a pathogen?
a disease causing micro-organism
e.g. bacteria, virus, fungi
bacteria cause disease by producing toxins
virus cause disease by dividing in cells causing them to burst
Body’s defence against pathogens?
I, Barriers (prevents pathogens entering the body)
II, Phagocytes (perform phagocytosis and stimulate specific response)
III, Specific Response (uses lymphocytes to produce memory cells and antibodies)
What are the Barriers (I)?
Skin, an impermeable barrier made of keratin
Cilia & Mucus in Lungs
Stomach Acid (denatures/breaks down pathogens)
Describe the process of Phagocytosis (II)?
pathogen releases chemicals
this attracts the phagocyte
the phagocyte binds to the pathogen
the phagocyte engulfs the pathogen
forms a phagosome around the pathogen
lysosomes inside the phagocyte release digestive enzymes into the phagosome
breaking down the pathogen by hydrolysis
Describe the Specific Response (III)?
phagocytes perform phagocytosis (engulf and destroy pathogen) without destroying the antigen, they place antigens on their surface, they present antigens
t lymphocytes (t cells) bind to the antigen and become stimulated
they divide by mitosis to form 3 types of cells: t helper, Cytotoxic T cells, t memory
t helper cells stimulate b lymphocytes (b cells)
cytotoxic T cells kill infected cells (infected by virus)
t memory cells provide long term immunity
b lymphocytes (b cells) engulf and present antigens on their surface, the t helper cells bind to this
the b cells become stimulated and divide by mitosis to make 2 types of cells: Plasma Cells & B Memory Cells
Plasma cells make antibodies
B memory cells provide long term immunity
What is a antigen?
a protein on the surface of a pathogen that stimulates an immune response
How does the immune response lead to production of antibodies?
the phagocytes stimulate the t cells, the t cells form t helper cells, the t helper cells stimulate the b cells, the b cells form plasma cells, the plasma cells make antibodies
What is an antibody?
a globular protein
made by plasma cells
has 3 regions: variable region, hinge region, constant region
variable region has a different shape in each antibody, contains the antigen binding sites, these bind to complementary antigens (on a pathogen) to form an antigen-antibody complex, destroying the pathogen
hinge region gives the antibody flexibility
constant region the same shape in all antibodies, binds to phagocytes to help with phagocytosis
How do Memory cells (B/T) work?
made during the specific immune response after a new infection by a pathogen (called a primary infection)
B and T memory cells remain in the blood
if person is reinfected by the same pathogen (called a secondary infection) the memory cells will recognise the pathogen and produce antibodies RAPIDLY and to a LARGE amount
therefore the pathogen is killed before it can cause harm = immunity
How does a vaccine produce immunity?
involves giving an injection that contains dead/weakened pathogens that carry antigens which stimulates the immune response leading to production of antibodies & memory cells
Active vs Passive immunity?
Active = individual has memory cells – can make their own antibodies & provides long term immunity
Passive = person given antibodies, these work then die, no long term immunity, no memory cells.
Active vs Passive immunity?
Active = individual has memory cells – can make their own antibodies & provides long term immunity
Passive = person given antibodies, these work then die, no long term immunity, no memory cells.
How does activity immunity occur?
naturally = by primary infection, artificially = by vaccination
How does passive immunity occur?
naturally = from mother to baby (placenta or breast milk)
artificially = by injection
Successful Vaccination Programme?
- produce suitable vaccine
- effective – make memory cells
- does not cause disease
- no major side effects
- low cost
- easily produced/transported/stored/administered)
- herd immunity
What is herd immunity?
when a large proportion of the population is vaccinated, therefore most people will be immune, only a few will not be a immune, increases chance of non-immune person coming into contact with immune person, so the pathogen has no where to go, so it dies out
Problems with Vaccination Programmes?
vaccine does not work (dead form ineffective, pathogen hides from immune system)
vaccine not safe (no weak/inactive form, causes major side effects)
many strains of pathogen
cannot achieve herd immunity (logistic of vaccinating large proportion)
antigenic variability
What is antigenic variability?
the pathogen mutates, the antigen changes shape, so the memory cells no longer complementary – do not recognise the pathogen, therefore the pathogen can reharm
What is a monoclonal antibody?
one type of antibody, complementary to one type of antigen, made by one type of plasma cell
What are monoclonal antibodies used for?
identify specific antigens or antibodies in person’s blood, or pregnancy tests
The ELISA test?
- apply sample to surface
- the antigens in the sample will attach to this surface
- wash the surface to remove any antigens that aren’t attached
- add the antibody that is specific to the antigen you are trying to detect
- leave to allow binding
- rinse to remove excess antibody
- add a second antibody that will bind with the first antibody
- the second antibody has an enzyme attached to it
- add the substrate to this enzyme (must be colourless)
- the enzyme acts on the substrate
- the substrate is converted into coloured products
- the amount of antigens present is relative to the intensity of the colour that develops
How are monoclonal antibodies used in pregnancy testing?
Pregnant Women produce HCG Hormone in their Urine
Test Strip has 3 parts to it (1st: start contains antibodies complementary to HCG, 2nd: middle contains antibodies complementary to HCG-Antibody complex, 3rd: end contains antibodies complementary to HCG Antibodies)
if woman is pregnant, HCG in the urine binds to antibodies on 1st part forming a HCG-Antibody complex, the HCG-Antibody complex then binds to antibodies on the 2nd part forming a blue line (positive result), HCG Antibodies also bind to 3rd part as a control
if woman is not pregnant, no HCG in urine so nothing binds to HCG Antibodies in 1st part, so nothing binds to antibodies in 2nd part leaving no blue line (negative result), the HCG Antibodies still bind to 3rd part for the control
What is HIV/AIDS?
HIV = Human Immunodeficiency Virus
AIDs = Acquired Immunodeficiency Syndrome
HIV is the Pathogen, AIDs is the Infectious Disease
HIV is spread by fluid to fluid contact (unprotected sexual intercourse, sharing needles, mother to child via placenta or breast feeding)
HIV damages and destroys T Helper Cells, therefore person no longer produces Immune Response and has no defence to against pathogens/infections = AIDs
With AIDs, individual at risk from all sorts of pathogens/infections called Opportunistic Infections
How does HIV infect host cells?
- P120 molecules on the HIV bind to CD4 receptor proteins on T helper lymphocytes and macrophages
- The protein capsid fuses with the cell membrane
- HIV RNA + enzymes enter the T cell
- HIV reverse transcriptase converts the virus’s RNA to DNA
- The new DNA is moved into the helper T cell’s nucleus where it is inserted into the cell’s DNA
- The HIV DNA in the nucleus creates mRNA using the cell’s enzymes
- This mRNA contains the instructions for making new viral proteins and the RNA from new HIV
- The mRNA leaves the nucleus of the host cell through nuclear pores and uses the cell’s protein synthesis mechanisms to make HIV particles
- The HIV particles bud away from the helper T cell with a piece of its cell surface membrane surrounding them, which forms their lipid envelope.
how can T ells distinguish invader cells from normal cells?
- phagocytes- they have engulfed the pathogen and have presented the pathogen’s antigen on their cell-surface membrane
- body cells- if they have been invaded by a virus they present some of the viral antigens on their cell-surface membrane
- transplanted cells- have different antigens on their cell-surface membrane
- cancer cells- they are different from normal body cells because they present antigens on their cell-surface membrane
