For any recipient, we must consider what antibodies they have. A patient with A positive blood has the following antibodies: anti-B For any donor, we must consider what antigens they have. The donor cannot have an antigen that matches the recipient's antibodies, or else agglutination will occur. Therefore, any B blood types will result in agglutination. The O positive person only expresses the Rh antigen, and the recipient does not express this antibody. No agglutination will occur.

We must first assume the two people are A, B, O compatible (ie., both patients are type A). An Rh negative person is negative because they lack the Rh antigen. An Rh positive person does not produce any Rh antibodies or else they would attack their own blood. Therefore, there is no antigen to attack and no antibodies to attack with, so agglutination will not occur.

Antibodies are produced by plasma cells (mature B-cells) with specific binding affinity for surface proteins that have been presented by antigen-presenting cells, like dendritic cells and macrophages. Once the plasma cell is stimulated by the presence of the specific antigen, it increases production of its antibody. These antibodies enter the blood and bind the antigen molecules on the surface of the pathogen cell. Cytotoxic T-cells and cytokines can then interact with the antibodies to initiate lysis of the infected cell or pathogen.

It helps to think of antigens and antibodies like a lock and key: they are highly specific for one another. B-lymphocytes create only one type of antibody. When this antibody attaches to an antigen presented by a macrophage or antigen-presenting cell, the B-lymphocyte will differentiate with the help of a helper T-cell. The result is replication of the B-lymphocyte to produce more of the same antibody from plasma cells and generate memory B-cells to easily respond in the event of a second infection by the pathogen.

The question specifies that the antibodies in question are serum antibodies, while IgA is primarily an antibody type secreted into luminal environments. As a result, we can conclude that IgA is not likely to be involved at all in this experiment. Beyond this, you must know that IgM is the type of antibody that is produced upon initial pathogen exposure. After CD4 cells facilitate isotype switching, IgG is produced and demonstrates more robust binding.

Blood antigens are the protein markers on the surface of red blood cells. On an A positive red blood cell, there is the A marker (antigen) and the Rh marker (antigen). Antibodies are found in the blood plasma, and these bind to foreign antibodies to cause agglutination. People produce antibodies for the antigens they do not have (Rh antibodies are only made after exposure to Rh positive blood). An A positive person will express the B antibody.

IgG is the only class of immunoglobulin that is able to cross the placenta. This is important as this immunoglobulin is able to provide passive immunity to the unborn fetus

Rh negative people are not born with Rh antibodies. After exposure to Rh positive blood, the Rh negative patient will begin producing Rh antibodies. Any subsequent exposure will cause agglutination. This has applications in childbirth, if there mother is Rh negative, and the baby is Rh positive. It is possible for the baby's blood to come in contact with the mother's (especially during childbirth). Neither the baby nor the mother are at risk, however, if the mother has another baby that is Rh positive, the mother will have antibodies from when she first encountered Rh positive blood from the previous baby. This may cause harm to the second (and any subsequent) Rh positive babies.

MHC I is found on all nucleated cells and presents antigens to cytotoxic T lymphocytes. These cytotoxic T cells contain CD8 receptors, which binds to MHC I. MHC II cells are found on B-lymphocytes and antigen presenting cells only. MHC II presents antigens to helper T cells, which contain CD4 receptors.

The epitope is the region of a target cell to which an antibody binds. The remaining choices are all structural regions of the antibody itself, as opposed to the target cells to which an antibody binds.