Immunity

What are the two types of defence mechanisms?

One type of defence mechanism is a non-specific response. This non-specific response is defined as a response which is [blank_start]immediate[blank_end] and the [blank_start]same[blank_end] for all pathogens. Example of this include a [blank_start]physical barrier[blank_end] e.g. skin or [blank_start]phagocytosis[blank_end]. Another type of defence mechanism is a specific response. This specific response is said to be a response that is [blank_start]slower[blank_end] and is [blank_start]specific[blank_end] to each pathogen. Some examples of a specific response is a [blank_start]cell mediated response[blank_end] (T lymphocytes) and a [blank_start]humoral response[blank_end] (B lymphocytes).

To defend the body from invasion what do the lymphocytes have to recognise?

Each cell has [blank_start]specific molecules[blank_end] on its surface that identify it which vary depending on its [blank_start]proteins[blank_end]. This is because proteins have a highly specific [blank_start]tertiary structure[blank_end]. Therefore, this variety of a specific [blank_start]3D[blank_end] structure allows for them to be separately identified. These protein molecules allow an organism to identify: 1) [blank_start]Pathogen[blank_end] e.g. HIV 2) [blank_start]Non-self[blank_end] material 3) [blank_start]Toxins[blank_end] produced by certain pathogens 4) [blank_start]Abnormal cells[blank_end] like cancer cells Although this is helpful, it is a disadvantage for those who have [blank_start]organ transplants[blank_end] as they believe it is non-self material. To help minimise this problem, donor are matched as closely as possible.

What are the two types of white blood cells?

Phagocytes [blank_start]Chemical[blank_end] products of pathogens or dead, damaged or abnormal cells act as [blank_start]attractants[blank_end], causing [blank_start]phagocytes[blank_end] to move towards the pathogen. Phagocytes have several [blank_start]receptors[blank_end] on their cell surface membrane that recognise chemicals on the pathogens. They [blank_start]engulf[blank_end] the pathogen to form a vesicle which is known as a [blank_start]phagosome[blank_end]. [blank_start]Lysosomes[blank_end] move towards the vesicle and fuse with it. Enzymes called [blank_start]lysozymes[blank_end] are present and destroy ingested bacteria by [blank_start]hydrolysis[blank_end]. The soluble products from breakdown are absorbed into the [blank_start]cytoplasm[blank_end] of the lysosome.

B lymphocytes (B cells) B cells mature in the [blank_start]bone marrow[blank_end]. They are associated with [blank_start]humoral immunity[blank_end], that involve [blank_start]antibodies[blank_end] that are present in [blank_start]body fluid[blank_end] or humour such as blood plasma. T lymphocytes (T cells) T cells mature in the [blank_start]thymus gland[blank_end]. They are associated with [blank_start]cell-mediated[blank_end] immunity that involves the body cells.

T lymphocytes can distinguish between their own cells and invader cells because: 1) [blank_start]Phagocytes[blank_end] have [blank_start]engulfed[blank_end] the pathogen and presented their antigens on their cell-surface membrane 2) Body cells are invaded by a virus and present their antigens on their cell-surface membrane 3) Transplanted cells from individuals have different antigens on their cell-surface membrane 4) Cancer cells are different from normal body cells and present them on the cell-surface membrane Cells that display foreign antigens on their cell-surface membrane are called [blank_start]antigen-presenting cells[blank_end].

Response of T Lymphocytes: 1) Pathogens invade body cells or are taken in by [blank_start]phagocytes[blank_end] 2) The phagocyte places antigens from the pathogen on its [blank_start]cell-surface membrane[blank_end] 3) Receptors on a specific [blank_start]helper T cell[blank_end] fit exactly onto these antigens 4) This attachment activates the [blank_start]T cell[blank_end] to divide rapidly by [blank_start]mitosis[blank_end] and form a clone of [blank_start]genetically identical[blank_end] cells The cloned T cells: a) Develop into [blank_start]memory cells[blank_end] that enable a [blank_start]rapid response[blank_end] to future infections b) Stimulate [blank_start]phagocytes[blank_end] to engulf pathogens by [blank_start]phagocytosis[blank_end] c) Stimulate [blank_start]B cells[blank_end] to divide and secrete their [blank_start]antibodies[blank_end] d) Activate [blank_start]cytotoxic T[blank_end] cells

What type of cells does humoral immunity produce?

Plasma cells secrete antibodies into the blood plasma and can make antibodies that lead to the destruction of the antigen.

Memory cells are responsible for a primary response and live for a brief duration.

B Lymphocytes 1) The [blank_start]surface antigens[blank_end] of an invading pathogen are taken up by a B cell 2) The B cell processes the antigens and presents them on its [blank_start]surface[blank_end] 3) [blank_start]Helper T cells[blank_end] attach to the processed antigens on the B cell activating them 4) The B cells is now activated to divide by [blank_start]mitosis[blank_end] to give a clone of plasma cells 5) The cloned plasma cells produce and secrete the [blank_start]specific antibody[blank_end] that exactly fits the antigen 6) The antibody attached to antigens on the pathogen and destroys them 7) Some B cells develop into [blank_start]memory cells[blank_end] that can respond to further infections

Antibodies are proteins with a specific binding site that have been synthesised by B cells.

Label the image of an antibody

Destruction of Antigens by Antibodies [blank_start]Agglutination[blank_end] of bacterial cells make it easier for phagocytes to locate the antigen as they are less spread out within the body. [blank_start]Neutralisation[blank_end] is when antibodies bind to the antigen to for a [blank_start]antigen-antibody complex[blank_end] which prevents them from infecting cells. Therefore they serve as [blank_start]markers[blank_end] to stimulate phagocytes to [blank_start]engulf[blank_end] the bacteria cells attached.

When using monoclonal antibodies an antigen is added to a well of the patients blood plasma which binds to the antibodies in their blood. A secondary antigen is added which attaches to the antigen and is then washed to get rid of unattached antibodies. A solution is added which changes colour with the enzymes that is present on the secondary antibody.

Which of these statements apply to passive immunity?

Which of these statements apply to active immunity?

Successful Vaccination For vaccination to be successful it must be [blank_start]economically available[blank_end] to immunise the most [blank_start]vulnerable[blank_end] population, have very few [blank_start]side effects[blank_end], have a means of [blank_start]storing[blank_end] and [blank_start]transporting[blank_end], have a means of [blank_start]administrating[blank_end] the vaccine and must be able to produce a [blank_start]herd immunity[blank_end] effect. However, vaccines don't eliminate disease as they may fail to [blank_start]induce immunity[blank_end] is certain individuals, may develop the disease immediately after a vaccination, the pathogen may mutate frequently ([blank_start]antigenic variability[blank_end]) or certain pathogens may hide from the immune system.

Label this diagram of HIV

Replication of HIV 1) HIV enters the [blank_start]bloodstream[blank_end] and circulates around the body 2) Proteins on the HIV readily bind to a protein found on [blank_start]helper T cells[blank_end] 3) The protein [blank_start]capsid[blank_end] fuses with the cell surface membrane and RNA and the [blank_start]enzymes[blank_end] enter the [blank_start]helper T cells[blank_end] 4) The HIV [blank_start]reverse transcriptase[blank_end] conversts the virus's RNA into [blank_start]DNA[blank_end] which is inserted into the [blank_start]nucleus[blank_end] 5) The nucleus creates [blank_start]mRNA[blank_end] containing the new instructions for [blank_start]viral proteins[blank_end] and [blank_start]RNA[blank_end] 6) The HIV particles break away with a piece of its cell surface membrane surrounding them which forms their [blank_start]lipid envelope[blank_end]