5.5 - Antibodies

Created by

Pietra Magagnin

Cards (37)

what are antibodies? 
proteins called immunoglobulin mode by plasma calls with specific binding sites that destroy specific antigens
how do antibodies destroy antigens?
cause agglutination of pathogens forming clumps so it's easier for phagocytes to find them
then they serve as markers to stimulate phagocytes to engulf cells to which they are attached
how agglutinins inactivate antigens 
cause antigens to bind together forming inactivated
how antitoxins inactivate antigens 
bind to toxins & neutralise them
how opsonin's inactivate antigens
tags foreign cells for destruction by phagocytes
what are antibodies made of?
4 polypeptide chains - 1 pair of long, heavy chains & 1 pair short, light chains
structure of antibodies - constant regions
same for all antibodies Of the same class
they bind to receptors on cells
Structure of antibodies - variable regions
forms the antigen binding sites that's different on different antibodies
structure of antibodies - antigen binding sites
each antibody has 2 so can bind to a pathogens at once
antibody recognises epitopes on antigen and binds to it forming an antigen- antibody complex
Structure of antibodies - hinge region
connects light and heavy chains through disulfide bonds so the two chains can open and close
what are monoclonal antibodies
antibodies artificially produced that are all genetically identical so bind to & destroy one specific antigen
uses of monoclonal antibodies
pregnancy tests
medical diagnosis
preventing rejection in organ transplants
targeting medication to specific cells
meaning of monoclonal antibodies 
mono: single/one
clonal: genetically identical
Why aren't blymphocytes used to make monoclonal antibodies 
if you take them out of the body they won't divide well
Making monoclonal antibodies 
Mouse exposed to non-self material corresponding to antibody needed
b-lymphocytes in mouse produce a mixture of antibodies which are extracted from the spleen of the mouse
b-lymphocytes are fused with myelomas (cancer cells) to form hybridomas
hybridomas are separated under a Microscope & each cell is cultured from a clone
clones producing antibodies needed are grown on a large scale I antibodies are extracted from growth Medium
antibodies undergo humanisation
who developed monoclonal antibodies?
Cesar Milstein and George Kohler
what does ELISA stand for?
enzyme linked immunosorbent assay
What's ELISA used for?
to detect an antigen in a sample of liquid using monoclonal antibodies
types of ELISA 
direct ELISA: uses one antibody complementary to antigen
indirect ELISA: uses 2 different antibodies
how ELISA works
liquid containing suspected antigen is placed into a well, of a plastic plate & left to adhere to plastic so becomes immobilised
complementary monoclonal antibody with enzyme tag is added to wells
plastic plate is washed so unbound antibody-enzyme molecules are washed away
substrate to enzyme is added which reacts to produce a colour change
intensity of colour indicates the quantity of antigen
controls in ELISA test
positive control
negative control
positive control in ELISA
contains antigen
if it doesn't change colour the test isn't working
negative control in ELISA test
doesn't contain antigen
if it changes colour it suggests contamination
what do pregnancy tests detect
HCG - human chorionic gonadotropin
how do pregnancy tests work?
application area contains mobile monoclonal antibodies with enzyme attached
When urine goes on application area HCG binds to antibodies forming antigen-antibody complex
mobile antibodies move up the stick by capillary action
test strip contains immobile monoclonal anti-HCG antibodies with the substrate attached
mobile HCG complex binds to antibodies on test strip & enzyme -substrate reaction creates a coloured line
in control strip there are immobile secondary antibodies that detect anti-HCG antibody & enzyme substrate complex generates a coloured line
what are monoclonal antibodies are used to detect
influenza
hepatitis
chlamydia
some cancers
HIV
diagnosing prostate cancer 
Men with prostate canur often produce more of PSA protein
by using monoclonal antibodies we can obtain a measure of the level Of PSA in the blood
targeting drugs to cancer cells
cancer calls have antigens called tumour markers that aren't Found on normal body cells
monoclonal antibodies that bind to tumour markers so block chemical signals that stimulate cell growth
indirect Monoclonal antibody therapy
radioactive or cytotoxic drug is attached to monoclonal antibodies
monoclonal antibodies bind to turnour Markers so release drug straight to cancer cells
side effects of using monalonal antibodies to treat cancer
they're reduced because anti-cancer drug only accumulates on cancer cell so no damage done to healthy cells
Why are monoclonal antibodies called magic bullets?
they only hill cancer cells
used in smaller doses - cheaper & reduces side effects
What's herceptin
a Monoclonal antibody that attaches to HER2 receptor proteins on cells to help T cells target them for destruction to treat breast cancer
HER2 protein 
produced by HER2 gene which is overexpressed by cancerous cells so they divide too much
how herceptin destroys cancer cells
herceptin recognises HER2 protein & attaches to it
t-lymphocytes recognise antibody as foreign & attack destroying the cell I reducing tumour
What monoclonal antibody is used to prevent rejection in organ transplant
OKT3
how does OKT3 work
it specifically binds to CD3 receptor on t lymphocytes so it no longer forms complexes with t lymphocyte receptor so it can no longer identify antigens so transplanted organ is safe from immune system
t-lymphocytes are still produced but don't have CD3 receptor
ethical issues regarding monoclonal antibodies
animal testing
human safety when used in treatments
genetic engineering-human genes transplanted into mine for humanisation
testing on humans