Specific response to infection
The immune system of the body has four key characteristics
The immune system of the body has four key characteristics
- It can distinguish ‘self’ from ‘non-self’
- It is specific – it responds to specific foreign cells
- It is diverse – it can an estimated 10 million different antigens
- It has immunological memory
- Lymphocytes
- They are made in the bone marrow of long bones
- They are involved in recognising and responding to foreign antigens
- Move freely through tissues
- B Cells
- Produced in bone marrow
- Found in lymph glands and free in the body
- B effector cells
- Cells divide to form the plasma clones cell
- Plasma cells
- Produce antibodies to particular antigens
- B memory cells
- Provides immunological memory to specific antigens
- T Cells
- Produced in bone marrow and mature in the thymus
- T cells have surface receptors
- T Killer cells
- Produce chemicals to destroy infected body cells
- T helper cells
- Activate the plasma cells to produce antibodies
- Secretes opsonins to label pathogen for phagocytosis
- T memory cells
- Long lived cells that make up immunological memory
- Can divide rapidly to form T killer cells
- Antigens being displayed on the cell surface membrane
- Proteins taken by vesicles to surface
- Become receptors on the surface of the phagocyte
- The humoral response of the immune system reacts to antigens found outside the body cells
- Results in production of antibodies
- T cells activate the B cells
- T helper activation
- When a pathogen enters the body chemicals produced will attract phagocytes
- When a phagocyte ingests a pathogen it becomes an Antigen presenting cell (APC) using undigested proteins
- A T cell has similar receptors on its surface which bind with the APC to produce more cells with the similar receptors
- These T cells become active T helper cells which are then used throughout the immune system with a remainder becoming memory cells if the same antigen is ever encountered again
- The effector stage
- B cells have specific immunoglobulins on their surface which bind to specific pathogens
- A B cell will engulf the pathogen by endocytosis, and digested in a phagolysosome. Some of the undigested matter will move to the surface and attach to the MHC
- A T helper cell from the active clone recognises the specific antigen displayed on the MHC complex
- This releases cytokines from the helper cells which stimulate B cells to divide and from clones, clonal selection.
- The plasma cells are produced, which produce a large amount of antibodies that are identical to the immunoglobulin of the parent B cell
- Antibodies will bind to a specific antigen on the particular pathogen which causes destruction in one of several ways
- Agglutination; When antibodies bind to the antigens on pathogens, the microorganisms clump together, this prevents them spreading and easier for them to be engulfed
- Opsonisation; The antibody acts as an opsonin, a chemical which makes an antigen more recognisable by phagocytes
- Neutralisation; Antibodies neutralise the effects of bacterial toxins by bonding to them
- Plasma cells live for only a few days, but as they can produce up to 2000 antibodies per second this can be very effective. They have many ribosomes
- If the pathogen is already inside a host cell the humoral response is not very effective
- The mediated response involves T killer cells which respond to specific antigens
- When a body cell is infected it is an APC
- T killer cells bind to matching antigens on the cell, which then if exposed to cytokines rapidly divide to form clones with the same antigen receptors
- These killer cells release enzymes to make pores in the membrane of the infected cells, this allows free entry of water and ions, lysing the cell
- Primary
- Involves the production of antibodies by the plasma cells produced from the B effector cells and the activation of T killer cells
- It can take quite a long time, meaning you may experience symptoms
- For the primary immune response the humoral response is fully done
- Secondary
- The secondary immune response is quicker, when the B APC cells divide they produce memory cells
- Memory cells from the primary immune response respond rapidly to the antigen for which they are an APC, these memory cells produce antibodies extremely quickly
- At the same time a clone of active T killer cells are formed which become memory cells which can turn into active T killer cells if they encounter the pathogen again