1. Anti-B (and anti-A) are in the IgM class. Thus they are pentamers, which are too big to pass through the placenta. Anti-D antibodies, by contrast, are monomers; being much smaller, they easily cross the placental barrier.

2. Lymphatic drainage from the right upper extremity passes through the right axillary region. If lymph nodes and lymphatic vessels are removed from this region, drainage from the extremity is reduced and tissue fluid accumulates there.

3. The antilymphocyte serum suppresses her immune system so her T cells will not attack the transplanted heart. Unfortunately, this makes a patient very susceptible to opportunistic diseases.

4. B cells require activation by helper T cells, which develop in the thymus. Therefore, a loss of thymic function impairs both the humoral and cellular immune responses, just as the destruction of helper T cells by the AIDS virus does.

5. A B cell contains very little cytoplasm or endoplasmic reticulum, whereas a plasma cell has a much greater cytoplasmic volume and extensive rough ER. This is consistent with the role of a plasma cell in rapidly synthesizing immunoglobulins.

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