Response to infection Flashcards
What do the non-specific immune response and the specific immune response make up?
The primary response
What are antigens?
Molecules (usually proteins or polysaccharides) found on the surface of cells
Which immune response happens first?
The non-specific immune response
What is the non-specific immune response?
It is non-antigen specific so occurs in the same way for all microorganisms regardless of the foreign antigen they have
What 3 mechanisms are part of the non-specific immune response?
- Inflammation at the site of infection
- Production of interferons (anti-viral proteins)
- Phagocytosis and lysozyme action
Non-specific immune response 1: describe inflammation at the site of infection
The site of infection becomes red, warm, swollen, and painful = inflammation
Non-specific immune response 1: how does inflammation work?
- The immune system recognises foreign antigens on pathogen surface and releases molecules that trigger inflammation
- Molecules cause vasodilation increasing blood flow to site = lots of immune system cells brought
- Molecules also increase permeability of blood vessels = allows immune system cells to move out of blood cells into the tissue
- Pathogen can be destroyed
Non-specific immune response 2: what do interferons do?
Interferons help prevent viruses spreading to uninfected cells
Non-specific immune response 2: how do interferons work?
- They inhibit the production of viral proteins which prevents viral replication
- They activate cells in the specific immune response to kill infected cells
- They activate other mechanisms of the non-specific immune response eg inflammation
Non-specific immune response 3: what is phagocytosis?
Engulfment of pathogens using phagocytes (type of white blood cell) which are found in the blood and tissues
Non-specific immune response 3: what cells are the first to respond to a pathogen in the body?
Phagocytes
Non-specific immune response 3: How does phagocytosis work?
- A phagocyte recognises antigens on the pathogen and engulfs it using the cytoplasm = phagocytic vacuole is formed
- A lysosome fuses with the phagocytic vacuole and the lysozymes break down the pathogen
- The phagocyte presents the pathogens antigens on its cell surface to activate other immune system cells
What is the specific immune response?
A response that is antigen specific that targets specific pathogens and involves T and B cells
Specific immune response: what type of cell is a B cell?
White blood cell covered with antigen-specific receptors
Specific immune response: how do phagocytes activate T cells?
- Receptors on T cells bind to complimentary antigens on antigen-presenting cells ie phagocytes = each T cell will bind to a different antigen
- The T cell is activated and divides to produce clones of itself
Specific immune response: what are the different types of T cells + explain?
T helper cells – release substances to activate B cells, T killer cells and macrophages
T killer cells – attach to antigens on a pathogen-infected cell and kill it
T memory cells – involved in immunity
Specific immune response: what type of cells are B cells?
White blood cells that are covered in proteins called antibodies that are specific
Specific immune response: what do antibodies do?
Bind to antigens to form an antigen-antibody complex
Specific immune response: how are B cells activated?
T helper cells activate B cells alongside an antibody of a B cell binding to an antigen
Specific immune response: what do activated B cells turn into?
They divide by mitosis into plasma cells (B effector cells) and B memory cells
Specific immune response: what are plasma cells?
Clones of B cells that secrete antibodies specific to an antigen into the blood which will form lots of antigen-antibody complexes
Specific immune response: describe the structure of an antibody
Antibodies are made of four polypeptide chains – two heavy and two light
Each chain has a variable region and a constant region
Specific immune response: what are the variable regions on an antibody?
They form the antigen binding sites and are complementary in shape to the particular antigen
Specific immune response: what are the constant regions on an antibody?
Allow binding to receptors on immune system cells eg phagocytes and is the same in all antibodies
Specific immune response: what is a hinge region?
Allows flexibility when the antibody binds to the antigen
Specific immune response: how many binding sites do antibodies have?
Two so an antibody can bind to two pathogens at the same time
Specific immune response: what three ways do antibodies help to clear infections?
- Agglutinating pathogens
- Neutralising toxins
- Preventing the pathogen binding to human cells
Specific immune response: describe how antibodies agglutinate pathogens
An antibody can bind to two pathogens at the same time causing them to become clumped together – then engulfed by phagocytes
Specific immune response: describe how antibodies prevent pathogens binding to human cells
When antibodies bind to antigens, they block the cell surface receptors that allow pathogens to bind to host cells
Specific immune response: what two types of antibodies are there?
- Membrane-bound antibodies = attached to the membrane of a B cell
- Secreted antibodies = free from any attachment
Specific immune response: how do the two types of antibodies vary in structure?
They have different heavy chain proteins, membrane-bound antibodies have an extra section that anchors them to B cell membrane
Specific immune response: what codes for two heavy chain proteins in an antibody?
Both heavy chain proteins are coded for by a single gene
Why is the primary response slow?
There are few B cells that can make the antibody needed to bind to the specific antigen
Immunity: what do T memory cells remember + what do they divide into?
T memory cells remember the specific antigen and will recognise it the second time around
They divide into the correct type of T cells to kill the cell carrying the antigen
Immunity: what do B memory cells remember? + what do they divide into?
They remember the specific antibodies needed to bind to the antigen
They divide into plasma cells that produce the right antibody to the antigen
What does it mean if a person is immune?
Their immune system can respond quickly to a second infection using a quick secondary response
What are the two types of immunity?
- Active immunity
- Passive Immunity
What is active immunity?
Immunity you get when your immune system makes its own antibodies after being stimulated by an antigen
What are the two types of active immunity?
- Natural = become immune after catching a disease
- Artificial = become immune after a vaccine
Active immunity: how do vaccines work?
They contain antigens that stimulate the primary immune response against a particular pathogen without causing disease = produces memory cells
What is passive immunity?
Immunity you get from being given antibodies from a different organism
What are the two types of passive immunity?
- Natural = when a baby becomes immune due to the antibodies it receives from its mother via placenta and breast milk
- Artificial = when you become immune after being injected by antibodies eg tetanus
What is the evolutionary race between humans and pathogens?
Over millions of years humans have evolved better immune systems whilst at the same time pathogens have evolved better ways to evade their hosts immune system
Describe HIVs evasion mechanisms that support the theory of an evolutionary arms race:
- HIV kills the immune system cells it infects which reduced overall number of immune cells which reduces its chance of being detected
- HIV has a high mutation rate in genes that code for antigen proteins which forms new strains = antigenic variation so immune system must produce a primary response for each new strain
- HIV disrupts antigen presentation in infected cells which prevents immune cells recognising and killing them
Describe mycobacterium tuberculosis’ evasion mechanisms that support the theory of an evolutionary arms race:
- M. tuberculosis produces chemicals that prevent the lysozyme fusing with the phagocytic vacuole when they are engulfed by pathogens so bacteria isn’t broken down and can multiply
- M. tuberculosis disrupts antigen presentation so immune cells can detect and kill infected phagocytes
Specific immune response: describe how antibodies neutralise toxins
Antibodies can bind to toxins produced by pathogens which prevents human cells being affected – toxin-antibody complexes are phagocytosed
