What is the diagnosis and the underlying clinical cause of these blood results? (60-year-old man with blood in stools, fatigue, weight loss, Hb 120 g/L, WCC 14.9 x 10^9/L, MCV 69 fL, Ferritin 18 ng/mL)

Correct Answer: B

Rationale: Step-by-step rationale for the correct answer (B): 1. Low Hb (120 g/L) and MCV (69 fL) indicate microcytic anemia. 2. High WCC (14.9 x 10^9/L) suggests an inflammatory response. 3. Ferritin (18 ng/mL) is low, indicating iron deficiency. 4. Symptoms of blood in stools, fatigue, weight loss are concerning for colorectal cancer. 5. Therefore, the correct diagnosis is iron deficiency anemia due to colorectal cancer. Summary of incorrect choices: A: Iron deficiency anemia due to poor diet - Ferritin levels would typically be low in this case, but other results do not support this choice. C: Vitamin B12 deficiency due to pernicious anemia - MCV is low, not high as expected in vitamin B12 deficiency. D: Thalassemia due to genetic mutation - Thalassemia would present with microcytic anemia

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.

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.