Question IV. You want to establish an experimental model to investigate complica

Question

Question IV. You want to establish an experimental model to investigate complications of blood transfusion. Thus, you immunize mice with a recombinant strain of Escherichia coli. This recombinant strain of Escherichia coli has been engineered to express a pattern of glycans normally found only on murine erythrocytes. One week after this immunization, you discover that the immunized mice are severely anemic. This observation can be best explained by the fact that [complete the sentence and assess each subsequent statement (36-39) as either factually correct (= “true”) or incorrect

(= “false”)]:
36. B cells in the immunized mice started to produce IgM antibodies, which bind to their own erythrocytes and induce complement-mediated lysis.

37. by immunizing the mice with a bacterium containing a self antigen, you have induced high levels of apoptosis in their developing B cells.

38. B cells in the immunized mice started to produce IgG antibodies, which bind to their own erythrocytes and induce Fc-receptor mediated uptake by phagocytes.

39. by immunizing the mice with a bacterium containing a self antigen, you have induced B cell somatic hypermutation and affinity maturation leading to splenomegaly.

Explanation / Answer

36. True. Once the recombinant bacteria start expressing glycans, B-cells are activated against those antigens that are not found on the erythrocytes of the mice. These B-cells initially produce Ig-M antibodies against the antigens on the bacterium. Since some of these antibodies cross react with micr erythrocytes also, complement mediated lysis occurs.

37. False. Since the bacteria express several antigens and not a single antigen, the mice immune system will react. However, those B-cell clones that produce antibodies against the antigens on mice erythrocytes may be anergized.

38. True. Initial immune response comprise of production of Ig-M antibodies. In a day or two, due to class switch, the mice immune system start producing high affinity Ig-G antibodies, which mediate destruction by phagocytes.

39. False. Affinity maturation and somatic hypermutation are not causes for splenomegaly. They are the normal mechanisms that lead to production of high affinity antibodies and memory B cells.

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