Immunity Flashcards
Features of non-specific defence mechanisms
- does not distinguish pathogen types
- response always the same
- act immediately
Features of specific defence mechanisms
- specific to a type of pathogen
- response dependent on pathogen
- takes time to produce antibodies/long lasting
Stages of phagocytosis
- attraction to pathogen by its chem. products + attachment
- pathogen ingested + phagosome formed (endocytosis)
- formation of phagolysosome (lysosome fuses w/ vesicle)
- digestion of pathogens by lysozyme through hydrolysis
- phagocyte either absorbs products or expels them (exocytosis)
T lymphocytes
- mature in thymus gland
- cell mediated immunity
Cell mediated immunity
- phagocyte presents pathogen antigen on membrane
- receptors on T.H cells fit antigen exactly
- attachment activates T cell replication -> clones
Cloned cells either:
- memory cells -> rapid future response
- stimulate phagocytosis
- stimulate B cell division + secrete antibodies
- activate T.C cells
Cytotoxic T cells (T.C cells)
produces perforin which makes holes in cell surface membrane -> permeable to many substances so cell dies
B lymphocytes
- mature in bone marrow
- humoral immunity
- concentrate in lymph nodes + spleen
Humoral immunity
- B cell processes antigen from pathogen membrane + presents it on its surface
- T.H cell attaches to antigens -> activate B cell
- B cell divides cloning plasma cells
- these produce + secrete specific antibodies for exact antigen of pathogen
- antibodies attach to antigen on pathogen, destroys it
- some B cells develop into memory cells -> divide rapidly, faster response to future infection
Differences between cell mediated and humoral immunity
- T cells, B cells
- no antibodies used in cell mediated
- pathogens identified by antigens floating in the blood in humoral vs. antigens on APC in cell mediated
Structure of antibody
- 4 polypeptide chains (2 heavy, 2 light)
- 2 identical variable regions (binding sites)
- constant region, bind to receptors of cells
- hinge protein, flexibility when binding
Functions of antibodies
- agglutination to clump bacterial cells -> easier for phagocytes to locate/destroy
- act as marker to stimulate phagocytosis
Monoclonal antibodies
Single type of antibody that can be isolated and cloned
-> used to target cancer cells by attaching to cancerous cell membranes and blocking chemical signals that stimulate uncontrolled growth
Passive immunity
caused by introduction of antibodies from outside source
- > immediate immunity
- > no direct contact w/ pathogen
- > no memory cells produced so not long lasting
Active immunity
stimulation of production of antibodies by own immune system
- > long lasting as memory cells produced
- > direct contact w/ pathogen
- > slower immunity
What is herd immunity and why is it important?
large proportion of population are vaccinated making transmission of pathogen difficult
-> important as it is never possible to achieve 100% vaccination
What do reverse transcriptase and integrase do in HIV replication?
reverse transcriptase - allows production of DNA from RNA (HIV is a retrovirus)
integrase - virus can insert new genetic material into nucleus/DNA of host cell
HIV replication
- HIV enters bloodstream, a protein readily binds to CD4 (common on T.H cells)
- capsid fuses w/ cell membrane -> RNA + enzymes enter T.H cell
- RNA -> DNA w/ rev. transcriptase
- new DNA inserted into T.H DNA w/ integrase
- DNA creates mRNA using cell enzymes which has instructions for viral proteins
- mRNA uses cell mechanism to make HIV proteins which break away w/ membrane that forms lipid envelope
Use of ELISA test
uses antibodies to detect presence + quantity of a protein eg. HIV, tuberculosis, hepatitis, allergens
very sensitive so detects v. small quantities of a molecule
Why are antibiotics ineffective against viruses?
- viruses lack own cell structures, so nothing for antibiotics to disrupt
- viruses have protein coat and no murein cell wall, no site to work at for antibiotics
How does HIV cause AIDS?
- kills and disrupts functioning T.H cells
- B cell cannot be stimulated to produce antibodies or secrete T.C cells
- immune system cannot respond effectively to other pathogens
Procedure for ELISA test
- apply sample to slide where antibodies will attach
- wash surface to remove unattached antigens
- add antibodies specific to antigen + leave to bind
- wash surface to remove excess antibodies
- add 2nd antibody w/ enzyme attached that binds to 1st
- add colourless substrate of enzyme, enzyme acts on it when bound -> colour change
- amount of antigen present relative to colour intensity
