what does each type of cell have?
each type of cell has specific molecules on its surface that identify it
what are the molecules on the surface of each type of cell?
proteins
why are proteins the molecules on the surface of each type of cell?
they have a highly specific 3D tertiary structure = unique
- antigen-antibody complex forms
what does the proteins on the surface allow the immune system to identify?
- pathogens
- cells from other organisms of the same species
- abnormal body cells
- toxins
what is a pathogen?
a microorganism that causes disease
what is an antigen?
foreign protein that stimulates an immune response
what is an antibody?
a protein specific to an antigen, which is produced by B cells
what is the effect of antigen variability?
antigen variability effects disease and disease prevention
what is meant by antigen variability?
- a pathogens DNA can mutate frequently
- if a mutation occurs in the gene which codes for the antigen, this causes the shape of the antigen to change
what does antigen variability cause?
- any previous immunity or memory B cells developed for a particular shaped antigen will no longer be effective
- the memory cells in the blood will only recognise the old antigen shape, so cannot destroy the pathogen
what is an example of antigen variability?
influenza virus mutates and changes its antigens quickly, so a new flu vaccine has to be created each year
explain the process of the phagocytosis of pathogens.
- the phagocyte recognises foreign antigen
- the cytoplasm of the phagocyte moves around the pathogen, engulfing it (by endocytosis)
- pathogen is now enclosed in a phagocytic vesicle
- the phagocytic vesicle fuses with a lysosome, the lysosome contains enzymes called lysozymes, which leads to the pathogen being digested
how does the phagocytosis of a pathogen lead to the presentation of antigens on its surface?
- the vesicle fuses with the lysosome
- the pathogen is digested by lysozymes
- antigen from pathogen are displayed on the cell membrane
what are T lymphocytes?
- mature in the thymus gland
- associated with cell-mediated immunity(involves body cells)
what is the role of antigen-presenting cells in cellular response?
- cells display foreign proteins on their cell membrane (antigen-presenting cells)
what is the process of T lymphocytes in response to infection by a pathogen?
- pathogens invade body cells or are taken in by phagocytes
- phagocyte places antigens from the pathogen on its cell-surface membrane
- receptors on the specific helper T cells bind to the antigens
- this attachment activates the T cell to divide rapidly by mitosis to form a clone of genetically identical cells
what can the cloned T cells turn into?
- develop into memory cells that enable a rapid response to future infections by the same pathogen
- stimulate phagocytes to engulf pathogens by phagocytosis
- stimulate B cells to divide rapidly and
form plasma cells which secrete antibodies - activate cytotoxic T cells
how do cytotoxic T cells kill infected cells?
- Tc cells kills abnormal cells and body cells infected by pathogens by producing the protein(perforin)
- perforin makes holes in the cell-surface membrane
what does holes in the cell-surface membrane mean?
membrane (of the infected cells)
becomes freely permeable to all substances and the cell dies as a result
what is the action of T cells most effective against?
- viruses
- viruses replicate inside cells
how do B lymphocytes respond to a vaccine?
- macrophages present antigens to the B lymphocytes
- the B cell would bind to a specific antigen, this is called clonal selection
- the B cell then rapidly divides by mitosis, this is called clonal expansion
- plasma cells produce monoclonal antibodies
- B plasma cells then develop memory cells against antigen in vaccine
