Hypersensitivity to penicillin and hypersensitivity to poison oak are both

Correct Answer: C

Rationale: Step 1: Hypersensitivity to penicillin and poison oak is due to hapten-protein complex formation. Step 2: Haptens are small molecules that bind to proteins, triggering an immune response. Step 3: This immune response can lead to sensitization and subsequent hypersensitivity reactions. Step 4: IgE antibody is typically involved in Type I hypersensitivity reactions, not haptens. Step 5: IgG and IgM antibodies are more associated with Type II and Type III hypersensitivity, not haptens. Step 6: Th-2 cells are involved in Type IV hypersensitivity reactions, not haptens. Summary: Choice C is correct as hypersensitivity to penicillin and poison oak is initiated by haptens, not IgE antibodies (Choice A), IgG and IgM antibodies (Choice B), or Th-2 cells (Choice D).

Correct Answer: B

Rationale: The correct answer is B because isotype switching involves the successive insertion of a single VH gene adjacent to different CH genes, leading to the production of antibodies of different classes. This process allows B cells to change the class of immunoglobulin they produce without altering the antigen specificity. Choice A is incorrect as it describes a mechanism different from isotype switching. Choice C is incorrect as it refers to the activation of genes on chromosome 6, which is not directly related to isotype switching. Choice D is incorrect as isotype switching specifically involves changing the heavy chain class of the immunoglobulin, not the light chain type.

Correct Answer: B

Rationale: The correct answer is B: cytotoxic hypersensitivity. Methyldopa can induce an autoimmune response causing hemolytic anemia by forming antibodies against erythrocytes. This type of reaction is characterized by the destruction of red blood cells by the immune system. The process involves antibody binding to the surface of red blood cells leading to their destruction by immune cells. A: Atopic hypersensitivity is commonly associated with allergies like asthma, hay fever, and eczema, not hemolytic anemia. C: Immune-complex hypersensitivity involves the formation of antigen-antibody complexes leading to inflammation but not direct destruction of red blood cells. D: Cell-mediated hypersensitivity involves T cell activation and is more associated with delayed responses like contact dermatitis, not acute hemolytic anemia.

Correct Answer: E

Rationale: I apologize, but it seems like there might be a mistake in the question as there is no option "E" provided. However, if we assume that the correct answer is missing and we need to select the affected immunoglobulin(s) due to the absence of J chains, the correct answer would be "C: IgA." J chains are essential for the polymerization and secretion of IgA antibodies. Without J chains, the production and secretion of IgA would be significantly impacted. IgG and IgM do not rely on J chains for their function, so options A, B, and D are incorrect in this context.

Correct Answer: D

Rationale: The correct answer is D: cytotoxic T cells. Cytotoxic T cells play a crucial role in graft and tumor rejection by directly targeting and killing foreign or abnormal cells. They recognize antigens presented on the surface of these cells and release cytotoxic molecules to destroy them. Non-complement-fixing antibodies (A) are involved in opsonization and neutralization but not the primary mediators of graft and tumor rejection. Phagocytic cells (B) such as macrophages can help in clearing cellular debris but are not as directly involved in targeting and destroying specific foreign or abnormal cells. Helper T cells (C) play a role in coordinating immune responses but are not the primary effectors in graft and tumor rejection.