Biology 1.6

Defence mechanismsnon-specificdo not distinguish between pathogens-barriers like skin-phagocytosisspecificunique response to each pathogen-cell-mediated response-humoral response

Phagocytosis

Chemical products of pathogen act as attractants Phagocytes attach to pathogen Phagocyte engulfs pathogen and forms a phagosome Lysosomes fuse with phagosome Lysosomes release lytic enzymes which break down pathogen soluble products are absorbed into cytoplasm Insoluble products released out of the cell by endocytosis 

T cells and Cell-mediated Immunity-Phagocytes that have engulfed pathogens show the pathogen's antigens on their surface-Infected body cells show antigens-Cancer cells show antigens1.Receptors on T helper cells fit onto antigens2.This activates other T cells to divide by mitosis 3.The T cells ...develop into memory cellsstimulate phagocytosis stimulate B cells to dividekill infected cells by making pores in membrane

B cell and Humoral Immunity1.Surface antigens of pathogen are taken up by B cells.2.B cells present antigens on their surface.3.T helper cells attach to B cells and activate them.4.The B cells are activated to divide by mitosis into plasma cells and memory cells.Plasma cellsSecrete antibodiesOnly survive for a few daysAntibodies attach to antigens and cause agglutination or lysis of pathogens.Memory cellsSurvive for decadesStay in the blood stream and stimulate a secondary immune response which involves fewer processes so is more rapid.

T cells are lymphocytes that mature in the Thymus gland.It is called cell-mediated immunity because it is stimulated by the antigens on the surface of body cells not pathogens

Antigenic variabilityAntigens are always changing. Therefore Immunity is not possible. 

AntibodiesFour polypeptide chainsTwo heavy chains (longer)Two light chains (shorter)A region which is the same in all antibodies(constant)A region which is unique(variable)

Monoclonal AntibodiesA single type of antibody that is extracted and cloned.-Separating a chemical from a mixture-calculating amount substance in a mixture-cancer treatment-transplant surgery

Passive ImmunityIntroduction of antibodies into individuals. Antibodies are not manufactured by that individual. Immunity is temporary.Active ImmunityAntibodies are produced by the individual so immunity is permanent.

A successful vaccine Economically available in large quantities Few side-effects if any Means of producing,storing and transporting Means of administering vaccine properly Possible to vaccinate the vast majority

Why vaccination may not work Fails to induce immunity in some Individuals may develop disease immediately after vaccine Pathogen may mutate frequently Too many varieties of one pathogen Certain pathogens 'hide' from body in cells or in small intestine Individuals may have objections to a vaccine

Problems with cholera Cholera is an intestinal disease and not easily reached by immune system Antigenic variability Mobile populations

Problems with Tuberculosis HIV lead to many people with defective immune systems Mobile populations who have poor accommodation Larger proportion of elderly people

Phagocytosis

Specific defence

Immunity