Question 1

An example of a qualitative precipitation procedure is:

Accepted Answer

Ouchterlony is a qualitative precipitation procedure that is commonly used in immunology to determine if a given antigen and a given antibody are compatible or not. The procedure involves placing drops of the antigen and antibody solutions in separate wells on an agar gel plate and allowing them to diffuse. If the two are compatible, a visible line of precipitation will form where the two meet. This is a qualitative test because it only tells you whether the two substances are compatible or not, not the exact amount of antigen or antibody present. The other answer choices are not examples of qualitative precipitation procedures.

Question 2

Radial immunodiffusion combined with electrophoresis best describes which of the following?

Accepted Answer

Rocket immunoelectrophoresis is a technique that combines radial immunodiffusion with electrophoresis to quantify antigens.

Question 3

In the Mancini endpoint method of RID:

Accepted Answer

In the Mancini endpoint method of radial immunodiffusion (RID), the area of the precipitin ring, which is proportional to the square of the diameter, is directly proportional to the concentration of the antigen.

Question 4

The strength of binding of one Fab on an immunoglobulin to one epitope on an antigen is referred to as:

Accepted Answer

Affinity refers to the strength of binding between a single antibody combining site (e.g. Fab) and a single epitope on an antigen. Inflammation and diapedesis are related to immune responses, but are not related to the strength of binding between an antibody and antigen.

Question 5

An Ouchterlony immunodiffusion assay is set up and a line of precipitation is seen forming between the antigen and antibody wells.The lines of precipitation formed by two adjacent antigen wells cross each other,forming an X.The reaction described is called:

Accepted Answer

In an Ouchterlony immunodiffusion assay, crossing lines (forming an X) indicate non-identity, meaning the antigens are different and do not share common epitopes.

Question 6

Which of the following might adversely affect an electrophoresis reaction?

Accepted Answer

All of the given options can adversely affect an electrophoresis reaction.

Decreasing the strength of the current can lead to slower or incomplete separation of the sample components. Changing the pH of the buffer can alter the charge on the sample molecules or the gel, leading to changes in the migration rate or band quality. Increasing the current beyond the recommended limit can generate excessive heat and cause irreparable damage or distortion to the gel, leading to inaccurate results. Therefore, all of these factors should be carefully controlled and optimized for a successful electrophoresis reaction.

Question 7

In which of the following zones is a false-negative reaction likely?

Accepted Answer

In the prozone zone, a false-negative reaction is likely to occur. This is because in this zone, the antigen concentration is so high that it saturates the available antibodies, preventing them from cross-linking and causing agglutination. This results in a negative reaction despite the presence of the antigen.

Question 8

Your supervisor wants you to design a quantitative precipitation assay for a new diagnostic test.Which of the following methods would you adopt?

Accepted Answer

Radial immunodiffusion is a quantitative method used to measure the concentration of antigens, making it suitable for a quantitative precipitation assay.

Question 9

Where does lattice formation occur to the greatest extent?

Accepted Answer

Lattice formation occurs to the greatest extent in the zone of equivalence, where the amount of antigen and antibody is balanced and forms large lattice structures. In the prezone, there is an excess of antigen, in the prozone there is an excess of antibody, and in the postzone, the antigen-antibody complexes have already formed and precipitated out of solution.

Question 10

When antibody combines with a particulate antigen,this is classified as which type of reaction?

Accepted Answer

When antibody combines with a particulate antigen, it results in the formation of visible clumps or aggregates, which is known as agglutination. The other choices are incorrect because precipitation occurs when soluble antigens are made insoluble, flocculation occurs when a soluble antigen is mixed with an antibody and forms visible aggregates or flocs, and turbidity refers to the cloudiness or haziness of a liquid due to the presence of suspended particles.

Question 11

The zone at which antibody and antigen are at optimal concentrations so that they form a large insoluble lattice together is called the:

Accepted Answer

The equivalence zone, also known as the zone of equivalence, is the point at which the concentrations of antibody and antigen are at their optimal ratio to form a large insoluble lattice, known as an immune complex. This results in the most efficient and effective binding of the antibody and antigen. The prozone and postzone are areas before and after the equivalence zone, respectively, in which the concentrations of antibody and antigen are too low or too high to efficiently form immune complexes.

Question 12

A situation in which antigen is in excess as compared to antibody is called:

Accepted Answer

The prozone phenomenon occurs when the amount of antigen in a sample is in excess as compared to the amount of antibody present. This results in decreased antigen-antibody complex formation and therefore, a false negative result in the test. In contrast, the postzone occurs when the amount of antibody is in excess as compared to the antigen, resulting in partial or complete inhibition of the test reaction, leading to false-negative or false-positive results. The equivalence zone represents the point at which antigen and antibody are present in equal amounts, resulting in optimal complex formation and a positive test result.

Question 13

A situation in which antibody is in excess as compared to antigen is called:

Accepted Answer

In the prozone, the number of antibodies is excessive as compared to the number of antigens. This leads to a weaker reaction between antigen and antibody because the excess antibodies can prevent the formation of antigen-antibody complexes that are necessary for the reaction. This can result in false-negative results in certain types of immunoassays. The postzone refers to a situation in which the antigen is excessive as compared to the antibody, and the equivalence zone refers to a situation in which the antigen and antibody are present in equivalent amounts and result in the strongest reaction.

Question 14

Which technique is best to determine if two fungal antigens are identical?

Accepted Answer

Ouchterlony immunodiffusion is used to compare antigens and determine their identity, partial identity, or non-identity by observing the patterns of precipitin lines formed in a gel.

Question 15

The initial force of attraction between an antigen and an antibody is called:

Accepted Answer

Affinity refers to the strength of the initial interaction between a single antigen-binding site on an antibody and an epitope (small, specific part of an antigen). It is determined by factors such as the shape, size, and chemical properties of the antigen and antibody combining sites. Avidity refers to the overall strength of binding between an antibody and multiple identical or nearly identical epitopes on a single antigen molecule or multivalent structure. Equivalence refers to the point at which all of the available antibody binding sites have been saturated by antigen, and no more binding can take place. Van der Waals forces are weak intermolecular forces that contribute to attraction between molecules or parts of molecules, but are not specific to antigen-antibody interactions.

Question 16

In radial immunodiffusion,the diameter of the precipitin ring correlates with the:

Accepted Answer

In radial immunodiffusion, the diameter of the precipitin ring formed around an antigen is directly proportional to the concentration of the antigen. Therefore, the correct choice is D, concentration of antigen. The other choices are incorrect as they do not correlate with the diameter of the precipitin ring in radial immunodiffusion.

Question 17

Affinity between individual antigen and antibody molecules depends on several types of bonds,such as ionic bonds,hydrophobic bonds,hydrogen bonds,and van der Waals forces.How is the strength of these attractions characterized?

Accepted Answer

The strength of the attractions between antigen and antibody molecules is characterized by avidity, which refers to the overall strength of binding due to multiple interactions between different binding sites. Specificity refers to the ability of an antibody to bind to a particular antigen, reactivity refers to the ability of an antigen-antibody complex to induce a biological response, and multivalency refers to the ability of an antigen or antibody to have multiple binding sites.

Question 18

The radial immunodiffusion test is a method involving:

Accepted Answer

The radial immunodiffusion test is a technique used to determine the concentration of an antigen in a sample based on its ability to form a visible ring of precipitation when it reacts with antibodies in a gel matrix. This method involves the process of precipitation, where the antigen and antibody form a complex that becomes insoluble and settles out of the solution. This setting leads to the formation of a ring, which is measured and used to calculate the concentration of the antigen. Therefore, Choice C (precipitation) is the best option.

Question 19

A serological reaction is set up in which the antigen and antibody are both soluble and form an insoluble complex that is detected macroscopically.What type of assay was described?

Accepted Answer

The description of insoluble complex formation that is detected macroscopically suggests a precipitation assay, where a soluble antigen and antibody form an immune complex that precipitates out of solution. Agglutination refers to the clumping together of cells, typically red blood cells or bacteria, in the presence of specific antibodies. Flocculation is similar but refers to the clumping of particles in a liquid suspension. Neutralization involves the inhibition of a biological activity by the specific binding and inactivation of a toxin or other agent. None of these options fit the description given.

Question 20

In an Ouchterlony immunodiffusion procedure,a continuous arc of precipitate is observed between two adjacent wells.This is a reaction of:

Accepted Answer

A continuous arc of precipitate between two adjacent wells indicates that the antigens in both wells are identical or nearly identical. This means that the antibodies in the serum are reacting with the same antigen in both wells. Therefore, the correct choice is A) identity.

Quiz 8: Precipitation Reactions