cell recognition and the immune system (2)
active and passive immunity
-herd immunity:
-if enough people in a population are vaccinated against disease, it is not possible for the disease to spread in a population, everyone is protected
-ethics of vaccination:
-since the time of Edward Jenner vaccination has always been controversial and many have ethical objections: (why)
-production and development involves use of animals
-side effects that cause long-term harm
-testing is difficult and side effects are unknown
-there are many calling for compulsory vaccination
-active immunity: having memory B-cells that are able to respond to specific antigen and produced plasma cells that produce antibodies
-passive immunity: having antibodies capable of binding to the antigen
-vaccination:
-the artificial introduction of disease antigens that activates immune responses and result in the production of memory B-cells
-vaccine types depending on how antigens have been obtained:
-attenuated or live vaccine
-inactivated or dead vaccine
-virus-like particle vaccine
-Edward Jenner:
1- 1796, pus from cowpox pustule from Milkmaid infected into 8-year old boy
2- later deliberately infected with smallpox
3- didn't contract smallpox
-due to similarity of two pathogens
-the Royal Society rejected his theory
-carried on experimenting with children (including own son)
-2 years later accepted for publication
-termed the vaccinations over "vacca" for cow in Latin
-Lois Pasteur:
-grew cholera in culture and infected chickens killing them
-if culture was kept and chicken survived they they were protected from new culture
-1881 - inoculated sheep with heat-treated Anthrax (survived)
-1885 - inoculated boy bitten by rabid dog with attenuated rabies (survived)
-attenuated vaccine - live vaccine:
- use of bacteria / virus with low virulence (multiplies at low levels):
-eg, measles and BCG
-inactivated vaccine - dead vaccine:
-eg, hepatitis A and cholera
-virus-like particle vaccination:
-virus proteins derived from structural proteins of virus
-proteins can assemble into virus-like Particles and lacks DNA:
-eg, HPV
HIV
monoclonal antibodies and ELISA
-monoclonal antibodies occur naturally as part of humoral immune response:
-each antigen that enters the body induces a specific B-lymphocyte to multiply and form a clone
-these clones produce identical antibodies complementary to a specific antigen
-production:
-antigen injected into mouse
-produces plasma cells with specific antibodies
-the plasma cell and tumour cell are fused to form a hybridoma
-the hybridoma will then produce an endless supply of monoclonal antibodies
-targeting cancer cells:
-direct monoclonal antibody therapy uses no toxic drugs:
-eg, herceptin binds to receptors on breast cancer cells preventing growth factors from binding
-indirect monoclonal antibody therapy with a radioactive / cytotoxic drug:
-when it attaches to the cancer cell it kills it
-these therapies require a much smaller doses of the drug and so are cheaper and have reduced side effects
-medical diagnosis:
-infectious diseases and some cancers can be diagnosed by identifying the presence of specific antigens or antibodies
-eg, influenza, chlamydia, prostate cancer
-ELISA test is used
-pregnancy testing:
-in pregnant women the placenta produces the hormone HCG which forms the basis of the test
1- HCG molecules carried up test in urine
2- HCG molecules bind to mobile antibodies making a antibody/HCG complex
3- the complexes bind to immobilised antibodies and enzymes catalyse reactions that result in a coloured compound to form a line indicating pregnancy
4- excess mobile antibodies bind to different immobilised antibodies, and the enzyme catalyses a reaction that results in a 2nd line, doesn't form due to pregnancy
-there are ethical issues surrounding monoclonal antibodies:
-welfare of animal test subjects
-making sure there is informed consent
-HIV:
-HIV is a retrovirus: contains RNA and a reverse transcript which enables the virus to produce DNA from RNA
-HIV is still a virus and therefore infects and reproduces in the same way
-AIDS:
-in HIVs later stages it causes Acquired Immune Deficiency Syndrome by killing or interfering with the normal functioning of T-helper cells
-the ultimate cause of death in AIDS patients is likely infection from another disease
-due to the lack of or because of the distraction of remaining T-helper cells
-antibiotics are ineffective against viruses:
-antibiotics work by inhibiting bacterial metabolic function:
-cell wall synthesis
-DNA replication
-protein synthesis
-viruses lack all of these functions / processes
-for example:
-penicillin: an antibiotic that inhibits enzymes involved in the synthesis of murein cell walls in bacteria, which weakens the cell wall and leads to cell death
-penicillin will not affect HIV as it doesn't have a murein cell wall
-the HIV process:
1- the gp120 glycoprotein on the surface of HIV attaches to cd4 and one of 2 coreceptors on the cd4+ cell, the viral contents enter by endocytosis
2- reverse transcriptase catalyses, first, the synthesis of a DNA copy of viral RNA and second, the synthesis of a 2nd DNA strand complementary to the first, the double stranded DNA then is incorporated into host DNA
3- transcritpion of DNA to RNA that then serves as the genome for new viruses and translated as to produce viral proteins
4- complete HIV particles are assembled, in macrophages, HIV buds out of the cell without rupturing it, in T-cells, HIV exits the cell by rupturing it, killing the cell