Antibodies in medicine + ELISA tests Flashcards
Monoclonal antibodies
Antibodies with the same tertiary structure produced from genetically identical plasma cells
So specific to one specific antigen
Monoclonal antibodies use in medical treatments
Anti cancer medication
Monoclonal antibodies use in medical testing
Pregnancy tests
ELISA tests
Monoclonal antibodies use in cancer treatment
MABs that are specific to tumour markers (antigen) on cancer cells so bind to cancer cells to be detected +diagnosed
And also attached to anti cancer drugs to kill cancer cell
What do pregnancy tests test for?
HCG protein which acts as antigen and it is only present in urine of pregnant women
Pregnancy test kit description
Application area = Has specific antibodies which are complementary to HCG bound to a coloured bead
Test strip = immobilised antibodies specific to hCG
What happens in case of a positive pregnancy test?
hCG from urine sample in application area binds to specific antibodies bound to beads (antibody-antigen complex)
Will move up strip to immobilised specific antibodies which binds to hCG and keeps it stuck with coloured beads
Why is there a colour change in a pregnancy test?
Because coloured beads bound to antibodies bound to hCG will be immobilised by binding to immobilised antibodies causing colour change
What happens in case of a negative pregnancy test?
No hCG bound to antibodies so immobilised antibodies will not bind to hCG so no colour change
What does ELISA test stand for?
Enzyme linked immunosorbent assay test
What do ELISA tests test for?
If there are antigens in patient using specific antibodies in the test (direct ELISA test)
If there are antibodies in patient using specific antigens in the test (indirect ELISA)
2 types of ELISA test
Direct
Indirect
Direct ELISAs test for?
A specific antigen in patient by using complementary antibodies in the test
Indirect ELISAs test for?
A specific antibody in patient using antigens in the test
Main reason ELISAs work?
Because it uses an antibody bound to an enzyme which when adding a substrate will form an enzyme substrate complex = colour change
Direct ELISA description if the test is positive
Place fluid sample from patient which contains antigen on well (immobilised)
Detection complementary antibody added attached to enzyme which binds to antigen (immobilised)
Wash
Add substrate which binds to enzyme = colour change
Direct ELISA description if the test is negative
Fluid sample is added but no antigen is present so not bound to well
Detection antibody with enzyme attached is added but will not be immobilised because no antigen present
So washed away
So when substrate added, no enzyme is present for E-S complex = no colour change
Why is the test well washed?
To remove any antibodies that were NOT immobilised to bottom of the well so if test was negative no colour change would be observed
Prevents false positives
When are indirect ELISAs used?
Mainly for HIV testing because HIV antigen usually hides in cells so hard to test for but the body produced HIV antibodies which are easier to test for
Indirect ELISA description if test is positive
HIV antigen is bound to well
Sample of plasma with different antibodies inc HIV one is added which binds to HIV antigen (immobilised)
Wash then add secondary antibody with attached enzyme which binds to HIV specific antibody
Wash again then add substrate which forms E-S complex = colour change
What happens if ELISA test is negative?
On washing, all antibodies are washed away so no HIV antibodies bound to antigen so no enzyme substrate complex formed when secondary antibody is added
Ethical issues of MABs
Uses animal products
Uses animal testing
Where are the antibodies bound to coloured beads found on the pregnancy test strip?
In the application area so immediately binds to antigen if present
In a positive pregnancy test, what causes a positive result
If the HCG antigen is present it is bonded to the coloured bead antibody
Then the immobilised antibody at the positive test zone binds to the ANTIGEN = SANDWHICH
In a pregnancy test, what causes the control zone?
Excess coloured bead antibodies not bound to antigen continue moving but immobilised by a different antibody further up the strip
