BIO 343 Lecture Notes - Lecture 9: Phagocytosis, Immune Complex, Extracellular Fluid

1. Neutralizing antibodies are effective at preventing
infection or toxicity mediated by pathogens or their toxic products. In fact, nearly all vaccines currently in use function by eliciting neutralizing antibodies. The most important feature of a neutralizing antibody is:
A. Having a high degree of multi-valency, such as being a pentamer or hexamer of immunoglobulin monomers
B. Having high affinity for the antigen
C. Being present at a high concentration in the circulation
D. Being efficient at activating the complement cascade
E. Having a long half-life in the body

2. IgM antibodies are much more efficient than IgG at activating the complement cascade. However, under certain circumstances, IgG antibodies will activate the complement pathway. One example of a situation in which IgG binding to its antigen will
NOT trigger the complement cascade is when:
A. The IgG antibodies bind to a multivalent soluble antigen in solution, such as a polysaccharide structure shed from a bacterial pathogen.
B. The IgG antibodies bind to a viral capsid protein that is present in more than 100 copies on the viral particle surface.
C. The IgG antibodies bind to a bacterial surface by recognizing a repetitive polysaccharide component of the bacterial capsule.
D. The IgG antibodies are binding self-antigens such as chromatin released from dead cells.
E. The IgG antibodies are neutralizing a bacterial toxin protein by blocking the receptor-attachment site on the toxin.

3. Antibody-dependent cell-mediated cytotoxicity (ADCC) is an important effector mechanism in immunity to virus infections. This immune pathway has also been exploited for clinical applications. For instance, patients with
various disorders, including rheumatoid arthritis and some B cell lymphomas, are treated with an antibody directed at CD20, a surface receptor expressed on all B cells. This antibody leads to the depletion of B cells from the patients by the actions of:
A. Natural killer (NK) cells
B. Cytotoxic CD8 T cells
C. Cytotoxic CD4 T cells
D. Activated macrophages
E. The complement cascade membrane attack complex

Topic A

1. Indicate to which branch(es) of theimmune system the following statements apply.

Explain your answer.

a) Involves macrophages

b) Responds to viral infection

c) Involves T cells

d) Responds to bacterial toxins

e) Most likely responds following an organ transplant

f) Involves cytotoxic T cells

g) Involves B cells

h) Involves complement

i) Responds to extracellular bacterial infection

j) Involves secreted antibody

k) Kills virus infected self cells

I) Involves the thymus

m) Involves the bone marrow

2. You are given two solutions, one containing protein A and theother the antibody to this protein both at about 5mg/ml. When youadd 1 ml of anti-A to 1 ml of protein A, a precipitate forms.However, when you dilute the antibody solution 20 fold and then mix1 ml of the diluted anti-A with 1 ml protein A, no precipitateforms.

Explain why no precipitate formed with the diluted antibody.

3. An energetic immunology student has isolated protein X.

The student believes it is a new isotype of humanimmunoglobulin.

a)What structural features would protein X have to have in orderto be classified as an immunoglobulin?

b) You prepare rabbit antibodies to (i) whole human IgG, (ii) tohuman λ chain and (iii) to human γ chain.

Assuming protein X is in fact a new immunoglobulin isotype,which of these antibodies will bind to protein X? Explain why?

TOPIC B

4. a) Describe the time course of a typical antibody response totetanus toxoid

b) Outline a vaccination schedule that makes effective use ofthis information.

5. a) Tetanus immunoglobulin from the horse can be used toprotect an individual against tetanus. How is the treatmentadministered and what are the advantages/disadvantages of this formof immunisation? 2

b) Is it possible to confer cell mediated immunity on anunsensitised recipient by transferring cells?

c) Would this be a practical method of immunisation, and whatproblems may be encountered in this type of experiment?

6. If you inject a rabbit with a large protein antigen X andsubsequently harvest the antiserum from the animal, would youexpect the antibodies to X in the antiserum to be monoclonal orpolyclonal?

TOPIC C

7. a) Why, if the immune system is so efficient, do we continueto suffer from infectious diseases?

b) Speculate on the consequences if the immune system were tolose its ability to distinguish self-antigens from foreignones.

c) If a child is born without a thymus gland, what will be thenature of the child's illness

d) If a child were born with a defect in the complement system,say a deficiency in function C3, what would be theconsequences?

8 Considering only combinational joining of gene segments andassociation of light and heavy chains, how many different antibodymolecules potentially could be generated from germ line DNAcontaining 500VL and 4JL gene segments and 200VH. 10DH and 4JH genesegments?

9 During an immune response to antigen, the antibodies producedduring a secondary and subsequent responses have a greater affinityfor antigen than those produced during a primary response toantigen

Explain what is meant by "affinity"

Explain in principle the mechanism which explains the aboveobservation re increasing antibody affinity for antigen insecondary and subsequent responses