The Immune Response

Flowchart nodes

• Body is invaded by a pathogen

• Phagocytes engulf pathogens

• - Recognises the antigens on the pathogen as non-self - Phagocyte engulfs the pathogen - Pathogen then contained in a type of vesicle called a phagosome - A lysosome joins with the phagosome to make a phagolysosome - Enzymes in the phagolysosome break down the pathogen, saving the antigens to present -Phagocyte becomes an APC (antigen-presenting cell)

• Formation of APC activates T lymphocytes which have receptors on their surfaces

• - Receptors bind to the antigens until they find a shape that is complementary - The T lymphocyte that has the complementary receptor is then chosen for mass production --> clonal selection - The clonally selected T lymphocyte the undergoes clonal expansion where it divides by mitosis LOADS

• Each new T lymphocyte differentiates into 1 of the 4 variants

• T helper cells --> release substances (such as interleukins) to active B lymphocytes and T killer cells

• T killer cells --> attach to and kill cells infected with virus

• T regulatory cells --> suppress the immune system when the threat is almost gone to prevent it attacking host's healthy body cells

• T memory cells --> remember the specific antigen and will recognise it again

• B lymphocytes are covered with antibodies : - Antibodies bind to antigens on the APC to find the one that's shape is complemtary - When they match, the B lymphocyte is clonally selected  - The selected B lymphocyte then undergoes clonal expansion --> divides by mitosis into plasma cells and B memory cells

• Plasma cells are clones of the B lymphocytes but can produce LOADS of antibodies

• B memory cells --> remember the specific antibodies that join to specific antigens

• Autoimmune diseases happen when these aren't right