Clinical Focus Question Consider the following situations and provide a likely diagnosis or appropriate response.
a. Six hours after receiving a dose of penicillin, a young child who has never been treated with penicillin develops a case of hives and diarrhea. The parents report the illness and ask if it might be an allergic reaction to penicillin.
b. A patient who has never taken sulfonamides but is known to be highly allergic to penicillin develops a bladder infection that is best treated with a "sulfa" drug. The patient wonders if "sulfa" drugs should be avoided.
c. A student who is unaware that he had developed a significant allergy to penicillin received an injection of the antibiotic and within minutes experienced severe respiratory distress and a drop in blood pressure. An alert intern administered epinephrine and the patient's condition improved quickly. Frightened but impressed by the effectiveness of the treatment, he asked the intern why the shot of adrenaline made him feel better.
d. A pet owner asks whether the same mechanism that causes his allergy to penicillin could also be responsible for his dog's development of a similar allergy to the drug. (Please go beyond yes or no.)
1. Indicate whether each of the following statements is true or false. If you think a statement is false, explain why.
a. Most antigens induce a response from more than one clone.
b. A large protein antigen generally can combine with many different antibody molecules.
c. A hapten can stimulate antibody formation but cannot combine with antibody molecules.
d. MHC genes play a major role in determining the degree of immune responsiveness to an antigen.
e. T-cell epitopes tend to be accessible amino acid residues that can combine with the T-cell receptor.
f. Many B-cell epitopes are nonsequential amino acids brought together by the tertiary conformation of a protein antigen.
g. Both TH and TC cells recognize antigen that has been processed and presented with an MHC molecule.
h. Each MHC molecule binds a unique peptide.
i. All antigens are also immunogens.
j. Antibodies can bind hydrophilic or hydrophobic compounds, but T-cell receptors can only bind peptide-MHC complexes.
2. What would be the likely outcome of each of the developments indicated below. Please be as specific as you can.
a. An individual is born with a mutation in C-reactive protein that enables it to recognize phospholipids in both bacterial and mammalian cell membranes.
b. A group of mice in which the CD1 family has been "knocked out" are immunized with Mycobacterium tuberculosis. Spleen cells from these mice are isolated and divided into two batches. One batch is treated with a lipid extract of the bacteria and a second batch is treated with a protein derived from the bacteria known as purified protein derivative (PPD).
3. Two vaccines are described below. Would you expect either or both of them to activate TC cells? Explain your answer.
a. A UV-inactivated ("killed") viral preparation that has retained its antigenic properties but cannot replicate.
b. An attenuated viral preparation that has low virulence but can still replicate within host cells.
4. For each pair of antigens listed below, indicate which is likely to be more immunogenic. Explain your answer.
a. Native bovine serum albumin (BSA) Heat-denatured BSA
b. Hen egg-white lysozyme (HEL) Hen collagen c. A protein with a molecular weight of 30,000 A protein with a molecular weight of 150,000
d. BSA in Freund's complete adjuvant BSA in Freund's incomplete adjuvant
5. Indicate which of the following statements regarding haptens and carriers are true.
a. Haptens are large protein molecules such as BSA.
b. When a hapten-carrier complex containing multiple hap-ten molecules is injected into an animal, most of the induced antibodies are specific for the hapten.
c. Carriers are needed only if one wants to elicit a cell-mediated response.
d. It is necessary to immunize with a hapten-carrier complex in order to obtain antibodies directed against the hapten.
e. Carriers include small molecules such as dinitrophenol and penicillenic acid (derived from penicillin).
6. For each of the following statements, indicate whether it is true only ofB-cell epitopes (B),only ofT-cell epitopes (T),or both types of epitopes (BT) within a large antigen.
a. They almost always consist of a linear sequence of amino acid residues.
b. They generally are located in the interior of a protein antigen.
c. They generally are located on the surface of a protein antigen.
d. They lose their immunogenicity when a protein antigen is denatured by heat.
e. Immunodominant epitopes are determined in part by the MHC molecules expressed by an individual.
f. They generally arise from proteins.
g. Multiple different epitopes may occur in the same antigen.
h. Their immunogenicity may depend on the three-dimensional structure of the antigen.
i. The immune response to them may be enhanced by co-administration of Freund's complete adjuvant.
Structure and Function
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