The interaction between pathogens and antibodies are non-covalent, and are comprised of weak intermolecular interactions. This question specifies that these interactions are reversible, which immediately eliminates covalent bonds as an option. Covalent bonding results in strong, long-term interaction on the atomic level. Dipole-dipole interactions and hydrogen bonding are more loose associations between full molecules, and can easily be broken in order for the molecules to dissociate.

Antibodies are not responsible for the removal of pathogens, only the binding and/or tagging foreign materials for destruction by other immune cells. Antibodies are released into the blood stream and bind to matching antigens on the surface of infectious cells. By binding and tagging foreign materials, antibodies enhance the ability of other immune cells (such as macrophages) to engulf or phagocytose the foreign material, leading to its destruction and removal.

Antibodies themselves cannot remove pathogens; they only aid in the removal of pathogens by immune cells.

The lack of antibodies indicates a failure of B-cell maturation, as B-cells are the only cells to produce antibodies. B-cells, as the passage indicates, are sent from the bone marrow directly into the circulation via arrow 2; thus, a breakdown in this process would be expected to lead to a loss of antibodies in the blood. Because the question states that the rest of the immune system is intact, we can assume that T-cell maturation is unaffected in the patient, meaning that arrows 1 and 3 are not affected.

Memory B-cells proliferate and remain in the body for great periods of time following an infection. These cells are used to respond to infections that have been previously seen by the immune system. They create antibodies for a specific antigen previously seen by the body.

All other answers are true statements. Each antibody responds to only a single antigen, and each plasma cell synthesizes only one type of antibody. B-cells differentiate into plasma cells when presented with a new antigen. Dendritic cells often act to present such antigens to T-cells and B-cells.

Once antibodies, produced by plasma cells, bind to the antigens on foreign bacteria or viruses, the complement system can begin to be assembled. The complement system is comprised of nine proteins that end up forming a pore in the membrane of bacteria and viruses, allowing other defense proteins to enter and destroying the sodium-potassium gradient that is required for energy generation in bacteria. Complement is also responsible for helping recruit immune cells to the site of infection or injury.

The major histocompatibility complex proteins are responsible for presenting antigens to helper T-cells.

Active immunization is that which occurs as a result of the immune response of the affected individual. Passive immunization is the passing of antibodies from one entity to another, such as a pregnant mother who passes antibodies through the placenta to the fetus. Artificial immunization occurs when one is exposed to the antigen of the infection without having to experience the infection. The antigen can be a weakened or dead form of the microbe. Natural immunity is achieved when one is infected by a live form of the microbe. In both natural and artificial immunity, the immune system generates antibodies and memory cells to fight off future infections.

In blood typing, the concern is avoiding the administration a blood transfusion that will be attacked by the body's immune system. For each antigen not present on the recipient's blood cells, there will be an antibody present in their blood stream. Therefore, someone who has type A blood will have an "anti-B" antibody. A transfusion of blood presenting the B antigen would be attacked and rejected by the type A individual's body. The Rh group (+/-) works similarly. Those who are Rh negative will have an antibody present to attack blood cells with the Rh group. Similarly, if someone is is Rh positive, there will be no Rh antibodies in his or her body and he or she could accept either Rh- or Rh+ blood. The patient in this question has type AB- blood, so he or she has no antibodies except for those that bind to Rh-positive blood. Therefore, all Rh-negative blood types are acceptable. (Type O blood signifies that the blood cells have no antigens present.)

Antibodies are made by B-cells, not T-cells. Monoclonal antibodies, as their name implies, are produced by a single clone of B-cells. In other words, a single B-cell is provoked to divide, producing a clone of identical cells. These cells then crank out one single type of antibody. These are monoclonal antibodies. Monoclonal antibodies only strongly recognize and bind to one specific antigenic site. The hCG molecule, being a polypeptide, may have multiple antigenic sites that can be recognized by antibodies, but a given set of monoclonal antibodies only recognizes one of these sites.

IgG (exists as a monomer in the blood) and IgE are both small enough to cross the placenta however, IgE is present in very low levels in the plasma.

IgE is the subclass of immunoglobulins that plays a critical role in the allergy response. IgE binds to allergens which in turn bind to Fc receptors on the mast cells, triggering the release of numerous inflammatory mediators, including histamine.