Immunity

Defence mechanisms Non specific Specific Immediate response slower response Same for all pathogens specific to each pathogen Physical phagocytosis cell-mediated humoral Barrier response response e.g. Skin T lymphocytes B lymphocytes

Phagocytosis Chemical products from a pathogen attract phagocytes. Phagocytes attach themselves to the surface of the pathogen. They engulf the pathogen forming a vesicle called a phagosome. Lysosomes move towards the phagosome and fuse with it.

Enzymes found in the lysosomes break down the pathogen by hydrolysis. Products of this breakdown are absorbed into the cytoplasm of the phagocyte.

Antigens An antigen is any part of an organism or substance that is recognised as non-self by the immune system and stimulates an immune response. For example – proteins that are part of the cell membrane or cell wall of invading cells such as microorganisms. The presence of an antigen triggers the production of an antibody.

T lymphocytes T lymphocytes respond to an organism’s own cells that have been invaded by non-self material e.g. a virus or a cancer cell. These cells present antigens on their cell membrane. T lymphocytes respond to this – Cell Mediated Immunity.

Response of T lymphocytes Once T cells have been activated they divide rapidly by .................... to form a ................ They develop into .................. cells that enable a rapid response to future infections by the same pathogen. They stimulate ....................to engulf pathogens. ................T cells stimulate ...............to divide. ...................T cells kill infected cells.

Antibodies

B cells Type of immunity = ......................immunity B cells present antigens from pathogen on their surface. They are activated by ................... cells. Plasma cells secrete .................. directly – primary immune response. ............... cells provide long term immunity.

Vaccination Active immunity – stimulates production of antibodies by individuals’ own immune system. Vaccination – introduction of a substance into the body with the intention of stimulating active immunity. Why is vaccination not always successful in eliminating a disease?