Unit 6- Response To Infection Flashcards
What cells are responsible for phagocytosis? 3
Phagocytes: neutrophils, monocytes and macrophages
How have phagocytes adapted?
Complex cytoskeleton that allows them to change shape
Contain lysozymes
Large
Describe phagocytosis:
- phagocytes move through blood/tissue fluid in response to chemicals
- they surround and engulf the foreign body (phagocytosis)
- microbes are trapped in phagosome which fuses with lysosome
- the lysozymes hydrolyse the microbe proteins, carbs and fats
Where do the different phagocytes work?
Neutrophils -blood
Macrophages and monocytes - tissue fluid/lungs and other spaces
What causes inflammation?
Granulocytes release chemicals (prostaglandins and histamines) which stimulates inflammation
What changes occur in inflammation? Name 4
- vasodilation
- capillary leakage (so phagocytes and granulocytes can enter)
- sensory neurone impulses (tender areas)
- blood clotting
- fever (the heat kills more pathogens than human cells)
- tissue repair (collagen deposits and stimulation of new cell growth makes scar tissue)
What make up the non-specific immune response?
Phagocytosis and inflammation
What cells make up the specific immune response?
B-lymphocytes and T-lymphocytes
How do we know the specific immune response is a later evolutionary advancement?
Only vertebrates have it as the cells that are involved are made in the bone marrow
What are antigens?
Clue: antigen is short for (ANTIbody GENerators)
Large molecules that bind to lymphocytes triggering a specific immune response
Which cell makes antibodies?
B-lymphocytes
What is an antibody?
A protein molecule that can bind specifically to an antigen
Structure of an immunoglobulin:
4 polypeptide chains (2 heavy and 2 light chains)
Joined by disulphide bonds to form a Y shape
They all have the same constant region (stem) and different variable regions (different amino acid sequences)
Which leads to a highly specific antigen-antibody complex
What is self recognition?
When cells are able to recognise the cell is not foreign by the distinct marker proteins (MHCs) on the cell membrane
What are receptors and where are they found?
They are proteins witch only 1 binding site (unlike antibodies 2) found on surface of T-lymphocytes
What do receptors do?
They bind to specific antigens forming an antigen-receptor complex
What is the main antigen presenting cell?
Macrophage phagocytes as they are in largest abundance
What is the macrophages role in the first step of infection from antigens?
In order to initiate the specific immune response a macrophage needs to engulf the pathogen and present the antigen on its surface becoming an antigen-present cell
What are cytokines and what cell releases them?
They are chemicals which stimulate clonal selection, released from macrophages and T-helper cells
Describe clonal selection from antigen presenting cell:
Eventually a helper T cell with a complementary receptor to the antigen will bind to antigen
The T helper cell releases cytokines which stimulate immature T and B lymphocytes to activate, proliferate and differentiate
The activated cells divide by mitosis making a clone army of cells with identical binding sites that is specific to the foreign antigen
How do T killer cells kill the infected cells?
- bind to antigens on infected cells
- secrete porin proteins
- porin makes pores in the cell membrane so water diffuses in
- the infected cell bursts (lysis)
What cells are part of cellular immunity?
Cytotoxic/killer T cells and memory T cells
Which cells are part of the humoral immunity?
B-lymphocytes which differentiate into thousands of plasma cells
Memory B cells
What is the job of plasma cells?
To synthesise antibodies specific to the antigens
Why is it called humoral immunity?
Because antibodies are being secreted into the blood plasma (humour)
How do antigens prevent infection?
- agglutination
- opsonisation (marking a pathogen for phagocytosis)
- binding to antigens on virus’ or bacteria prevents them attaching to host cells (blocks antigens)
- precipitation, binding to free soluble toxin proteins (blocking/changing their shape) making them insoluble
- lysis
Why do some of the activated B and T cells divide into memory cells?
Memory cells remain in the blood for years
- if the same antigen is encountered again memory cells divide quickly into plasma cells and killer cells
- this skips clonal selection
- secondary immune response
What is antigenic variability?
When pathogens develop new strains with different antigens
- due to mutation
- we cannot become immune
What is vaccination?
- injecting a person with a modified non-virulent strain to promote a primary immune response and make memory cells to that specific antigen
- when the real strain invades the secondary immune response will be able to recognise and kill it quickly
What is active immunity?
Any process that promotes a primary immune response leaving memory cells
Eg. Vaccination or catching a disease
What is passive immunity?
When antibodies are received
Eg. Breastmilk or across the placenta
When does passive immunity happen naturally?
When antibodies are passed across the placenta to the baby
In breast milk
When does passive passive immunity happen artificially?
Achieved through injection of antibodies in an antiserum
Eg. To combat AIDS
Why could some people not receive vaccines?
- newborns with weak immune systems
- people with immunosuppressant diseases
- those undergoing chemotherapy
What is herd immunity?
When the majority of a population (85-95%) are vaccinated, so there are not enough hosts for the disease to survive and reproduce
What are free riders?
People who choose not to get vaccinated compromising the threshold for herd immunity
What are T suppressor cells?
Cells that stop the response when an antigen has been removed, so the response doesn’t get too over the top and you begin wasting resources
Purpose of T helper cell?
To stimulate a specific immune response
Explain how the non specific immune response protects against infection by bacteria
- bacteria don’t have MHCs so are recognised as foreign
- phagocytes engulf the bacteria
- neutrophils engulf and digest bacteria
- monocytes become macrophages which also ingest and digest bacteria
- they release cytokines to attract other phagocytes to site of infection, increasing blood flow and inflammation
Describe the interaction of immune cells in producing a hormonal response
- macrophages present antigen to activate T helper cells
- T helper cells activate B cells by recognising antigen and producing cytokines
Similarities of humoral and cell mediated response
- both are specific to an antigen
- both require the formation of APCs and the presence of MHCs
- both involve clonal selection which is activation of only those cells which recognise the antigen
- both involve differentiation of cells, following activation by T helper cell
