In the bone marrow, RBC precursors are located:

Correct Answer: D

Rationale: The correct answer is D because RBC precursors are located surrounding macrophages near the sinus membrane in the bone marrow. This location allows for the interaction between macrophages and developing RBCs, facilitating the removal of nuclei from maturing RBCs. Choices A, B, and C are incorrect because RBC precursors are not typically found in the center of hematopoietic cords, adjacent to megakaryocytes, or surrounding fat cells in apoptotic islands in the bone marrow.

Correct Answer: B

Rationale: The most likely diagnosis for the patient is B: Hodgkin lymphoma. The symptoms of fever, night sweats, and painful lumps in the neck/armpits are classic signs of Hodgkin lymphoma. The Reed-Sternberg cells seen in Hodgkin lymphoma are characteristic and differentiate it from non-Hodgkin lymphoma. Infectious mononucleosis typically presents with sore throat and fatigue, not painful lumps. Tuberculosis usually manifests with respiratory symptoms. Non-Hodgkin lymphoma may present similarly, but the presence of Reed-Sternberg cells points towards Hodgkin lymphoma.

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: D

Rationale: The correct answer is D because a single B lymphocyte can produce antibodies of many different specificities due to the process of somatic hypermutation and class switching. This allows for the generation of a diverse repertoire of antibodies. Plasma cells, on the other hand, are derived from B cells and are typically monospecific, producing antibodies of a single specificity. This is important for maintaining a focused immune response. Explanation of other choices: A: Choice A is correct. Humans can indeed generate antibodies with approximately 10^8 different VH x VL combinations, contributing to the vast diversity of the immune response. B: Choice B is correct. A single B cell can switch from producing IgM antibodies to IgA antibodies through the process of class switching, enhancing the adaptability of the immune response. C: Choice C is correct. Hematopoietic stem cells possess the genetic potential to create over 10^4 immunoglobulin genes, which allows for the production of a wide array of antibodies

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.