11. Immunity Flashcards
What are antibodies?
- glycoproteins – immunoglobulins
- made by specialised lymphocytes
- responds to a specific antigen of complementary shape
What are the types of phagocytes?
neutrophil:
* released in large numbers from stores
* short-lived cells – die after killing and digesting a few pathogens
* dead neutrophils collect at a site of infection – form pus
* in blood, squeeze through capillaries
macrophage:
* larger
* found in organs and lymph nodes
* travel in blood as monocyte, settle in organs and develop into macrophages
Describe phagocytosis
- cells under attack release chemicals – histamine
- histamine and any chemicals released by pathogens attract neutrophils – movement toward chemical stimulus: chemotaxis
- neutrophils destroy pathogens engulfing them
- pathogens covered in antibodies further stimulate neutrophils – receptor proteins recognise and attach to antibodies
What are the types of lymphocytes?
B-lymphocytes:
* remain in bone marrow until mature
* spread throughout the body
* concentrated in lymph nodes and spleen
T-lymphocytes:
* produced in bone marrow
* mature in thymus
* doubles in size between birth and puberty
* shrinks after puberty
What are the features of lymphocytes?
- only carry out immune responses when mature
- each type of B- and T- lymphocyte is specialised – whole immune system responds to almost any pathogen
- mature lymphocytes circulate between blood and lymphatic systems – distributed throughout the body
How do B-lymphocytes work?
- B cell uses part of antibody molecule to make receptor on cell surface membrane
- antigen enters body – specific receptor selected = clonal selection
- specific receptor stimulated to divide by mitosis – huge numbers of identical B cells produced over a few weeks = clonal expansion
- some activated B cells become plasma cells or memory cells.
What are plasma cells?
- primary immune response
- activated B-lymphocyte cells
- produce and secrete antibodies – into blood, lymph, linings of lung and gut
- very fast rate of production – several thousand/sec
- short lived
- secreted antibodies stay in blood for longer until eventual decrease in concentration
What are memory cells?
- secondary immune response
- cells remain circulating in the body for a long time – last many years
- reintroduced antigen – cells divide rapidly = more plasma and memory cells
- invading pathogens can be destroyed and removed before development of any symptoms
- response is much faster – more antibodies produced, almost immediately after detection
What are the 6 different functions of antibodies?
- combine with viruses – prevent entry and damage to host cell
- attach to flagella of bacteria which makes them less active – easier for phagocytes to engulf
- have multiple antigen binding sites – agglutination of bacteria: reduces risk of spreading
- create holes in cell walls of bacteria – causes lysis
- coat bacteria, easier for phagocytes to engulf – receptor proteins for constant regions of antibodies.
- antitoxins: combine with toxins – neutralise antigen
How do T-lymphocytes work?
T-cell receptors:
* specific to 1 antigen
* activated during antigen presentation
T cells undergo clonal selection and clonal expansion.
T-helper cells:
* release cytokines: stimulate B cells, stimulate macrophages to carry out phagocytosis more vigorously, and stimulate T-killer cells to divide and differentiate by producing toxin-filled vacuoles
T-killer cells:
* search the body for invaded cells that are displaying foreign antigens on cell surface membranes
* recognise antigen
* attach to surface of invaded cells
* secrete toxic substances e.g. hydrogen peroxide
* kills body cells and containing pathogens
- memory T-helper and T-killer cells are produced – become active very quickly during secondary response
What is active immunity?
- body makes its own antibodies
- activation of lymphocytes occurs naturally during infection – natural active immunity.
- vaccination – artificial active immunity
- long term immunity
- takes time – ineffective against fast-acting, fatal diseases
What is passive immunity?
- antibodies not produced by body – not activated B and T cells
injection of antitoxin – artificial passive immunity
* antibodies collected from blood donors recently vaccinated against the disease
* provides immediate protection
* temporary – non-self antibodies, eventually removed from circulation by phagocytes
antibodies passing from mother to fetus through placenta – natural passive immunity
What is an example of natural passive immunity?
Colostrum
* produced by a new mother’s breasts
* contains antibody IgA
* remain on the surface of infant’s gut wall – prevents growth of bacteria and viruses
* pass into blood undigested – circulates in blood
What is a vaccine?
a preparation containing antigens that stimulates an immune response artificially.
* can contain live, dead, or harmless version of a microorganism, or a harmless version of a toxin i.e. a toxoid, or a preparation of surface antigens.
What are monoclonal antibodies (Mabs) and their usages?
antibodies made by a single clone of hybridoma cells – identical variable regions = specific to one antigen
- used for diagnosis and treatment
What are hybridoma cells?
cells formed by the fusion of plasma and cancer cells – secretes antibodies AND divides by mitosis
