Question 3: (5 points) An infant is admitted to the hospital with a history of r

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Question 3: (5 points) An infant is admitted to the hospital with a history of recurrent and persistent bacterial infections. His physician suspects he has an immunodeficiency disease, and obtains a sample of the patient's peripheral blood. The white blood cells are analyzed by antibody staining followed by flow cytometry, and the results are shown in figure A on the left. To determine the origin of the peripheral blood cell defect, a bone marrow biopsy is taken from the patient and compared to a healthy control, as shown in figure B on the right. Healthy infant Healthy infant Peripheral blood cells Bane marow cells ??? C03 CD19 (B cells CD19(Bcels) obtain To additional information, bone marrow cells are treated with a chemical that permeabilizes the cell membrane, allowing antibodies to enter the cells and bind to their target antigens within the cells, a technique known as 'intracellular staining'. The results of this analysis are shown in figure C D. Healthy infant Healthy intant Intracellular staining of bone marrow cells a). What are populations 1, 2, and 3 in Figure C? Explain your reasoning just a few words should be sufficient). (1.5 points) b). In another experiment, the expression.of proteins onthe surfaceof.cells froma bealthy infant are also examined. What is the population of cells that are IgMolgrnegs indicated by the arrow in figure D? Explain your reasoning (0.5 point) c). Based on these data, where (in terms of the stages of B cell development) does the defect seem to be occurring? Based on the events that occur in the different stages, explain what you think is most likely causing the block between these stages (2 point)

Explanation / Answer

a) The population 1 in the Figure C are the cells that express both IgM and Igk antibodies in low amount. Both the anibodies in those cells have lower scattering in the flow cytometry.

The population 2 are the cells that express IgM antibody in larger amount and Igk in lesser amount. IgM antibodies have higher scattering than the Igk in the cell population.

The population 3 are the cells that express both antibodies IgM and Igk in larger amount. Both the antibodies show higher scattering in the flow cytometry.

b) In the healthy individual, the cells shown by the arrow are those cells that have low expression of antibodies on the cell surface. This suggest that those are not affected by any antigens.

c) The B cells stages expressing higher IgM and Igk are affected by the pathogens in the patient. Lack of B cells expressing higher amount of antibodies is the cause of the immunodeficiency disease in the patience. It allows the bacteria to cause recurrent and persistent infections.

d) Lack of Igk antibody molecule is responsible for the patient's immunodeficiency disease. This is because all other anibodies molecules expression shown in the Western blots have similar expression in both the control and patient's bone marrow cells.

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