Module 3: Antigen-Antibody reactions

Question 1

5 antigen-antibody reactions

Answer 1

neutralization
agglutination
precipitation
complement fixation
Sensitization (opsonization)

Question 2

Neutralization

Answer 2

when antigen is bound to an antibody the activity of antigen may be neutralized or inhibited

Question 3

Agglutination

Answer 3

Used in TM lab

If RBC has the A antigen, the cell will react with anti A antisera to form agglutinates

Question 4

Precipitation

Answer 4

soluble antigen when combined with an antibody may precipitate out
Can be seen and measured to quantitate the amount of antigen present

Question 5

Complement fixation

Answer 5

in lab, if complement fixation proceeds to completion, the end result is hemolysis (visible)

in pt, antibody binds to antigen on a cell surface and can activate complement

Question 6

Sensitization (opsonization)

Answer 6

In vivo- antigen/antibody binding promotes phagocytosis

in vitro- sensitization not visible; use an additional antibody (antihuman globulin) to bridge the gap between antibodies coating the antigen, producing visible agglutination

Question 7

Antigen and antibody are held together by

Answer 7

forces acting together to keep the complex stable

Ionic bonding (oppositely charged groups)
Hydrogen bonding (electronegative atoms for hydrogen)
Van der Waals forces (weak attraction between electron cloud of an atom and the protons of the nucleus of other atom)
Hydrophobic forces (attraction of non-polar groups to one another)

Question 8

Affinity

Answer 8

the strength with which the idiotype grabs onto the epitope

Question 9

factors affecting the affinity constant

Answer 9

pH (optimum 6.5-7.5)
Ionic strength of reaction solution (Lower ionic strength = increased rate of association between Ab and Ag)
Concentration of reactants
Temp
Incubation time

Question 10

Avidity

Answer 10

the overall binding energy between multivalent antibodies and multivalent antigens

Question 11

Prozone

Answer 11

concentration of antibody exceeds that of antigen and lattice formation does not occur

Question 12

postzone

Answer 12

the concentration of antigen exceeds that of antibody and lattice formation is impossible

Question 13

zone of equivalence

Answer 13

in between prozone and postzone layer where antibody and antigen concentration are proportionate and a lattice is formed
Maximum precipitation occurs in this zone

Question 14

heterophile antibodies

Answer 14

a group of cross-reacting antibodies. These antibodies are produced in response to one antigen, but also react with an unrelated but structurally similar antigen

Question 15

Elution

Answer 15

the process of removing and antibody from and antigen in vitro

Question 16

4 different processes of elution

Answer 16

changing pH
increasing ionic strength of the solution
heat
organic solvents

Question 17

Antibody titre

Answer 17

determines relative concentration of an antibody in a serum sample
The reciprocal of the last dilution to visibly demonstrate the antibody