<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A 48-year-old man is being evaluated for an acquired defect of the myeloid stem cell line with a mutation in the PIG-A gene. His diagnosis was first suspected due to anemia and recurrent pink-tinged urine. Which of the markers will be negative in the flow cytometry test for his condition?? A: CD19, B: CD18, C: CD40L, D: CD55, E: CD3,  <response>: This question is asking about a patient with paroxysmal nocturnal hemoglobinuria PNH, which is caused by a mutation in the PIG-A gene. This leads to a defect in glycosylphosphatidylinositol GPI anchor production, which attaches proteins like CD55 and CD59 to the cell membrane. The absence of these GPI-linked proteins leads to complement-mediated hemolysis, causing the anemia and hemoglobinuria described. Of the answer choices, CD55 is a GPI-linked protein that would be absent in PNH. The other markers CD19, CD18, CD40L, CD3 are not GPI-linked and would be present.D: CD55 