How Do Polyclonal Antibodies Work?

Polyclonal antibodies are a class of drugs used to prevent and treat kidney transplant rejection and aplastic anemia in patients unsuitable for bone marrow transplantation. Aplastic anemia is a rare, serious blood disorder that occurs when the bone marrow (sponge-like tissue within the bones) cannot make enough new blood cells for the body to work normally. Polyclonal antibodies are secreted by different B cell lineages within the body. They are a collection of immunoglobulin (Ig, antibodies) molecules that react against a specific antigen (bacteria and viruses). The classical representation of an antibody is a Y-shaped molecule comprising four polypeptides-two heavy chains and two light chains. Each tip of the “Y” contains a paratope (a structure analogous to a lock) that is specific for one particular epitope (similarly, analogous to a key) on an antigen, allowing these two structures to bind together. These antibodies can be classified into two primary types (monoclonal and polyclonal) depending on how they are formed from lymphocytes (a type of white blood cells made in the bone marrow and a part of the immune system).

Polyclonal antibodies are composed of purified gamma globulin containing primarily IgG against human thymus lymphocytes. It is prepared by inoculating a horse with an antigen (human thymoyctes) which then induces the B-lymphocytes of the horse immune system to produce IgG immunoglobulins specific for that antigen. This results in polyclonal IgG that is then purified from the horse's serum to produce a usable drug product for immunosuppression.

The advantages of polyclonal antibodies include the following:

• Inexpensive
• Quick production
• Highly stable and tolerant of pH (quantitative measure of the acidity or basicity of aqueous or other liquid solutions) or buffer changes
• High ability to capture the target protein
• High affinity (quicker binding to the target antigen)
• Tolerant of minor changes of antigen
• Polyclonal antibodies are prescription-only medicines and are administered intravenously (through a vein) for approximately 8 to 14 days.

Polyclonal antibodies work in the following ways:

• They target various immune system proteins including lymphocyte surface proteins, granulocytes, platelets, bone marrow cells, and other cell types.
• They suppress the immune system to prevent renal transplant rejection.

Polyclonal antibodies are used in the following conditions:

To prevent and treat:

• Renal allograft rejection
• Skin allograft rejection
• Aplastic anemia (a condition that damages stem cells in the bone marrow)

Some of the common side effects include:

• Headache
• Fever
• Rash
• Chills 
• Diarrhea
• Nausea
• Vomiting
• Malaise (a sense of unease or a lack of well-being)

Other rare side effects include:

• Leukopenia (low white blood cell count)
• Arthralgia (joint pain)
• Thrombocytopenia (low blood platelet count)
• Dizziness (feeling faint, weak, or unsteady)
• Tachycardia (a fast heart rate—more than 100 beats per minute)
• Night sweats
• Anaphylaxis
  • Hypotension (low blood pressure)
  • Respiratory distress (difficulty in breathing)
  • Pain in the chest/back
  • Hyperglycemia (high blood glucose levels)
• Allergic reactions
  • Rash
  • Hives (itchy, raised welts that are found on the skin)
  • Itching
  • Swelling of face, lips, tongue, or throat

Information contained herein is not intended to cover all possible side effects, precautions, warnings, drug interactions, allergic reactions, or adverse effects. Check with your doctor or pharmacist to make sure these drugs do not cause any harm when you take them along with other medicines. Never stop taking your medication and never change your dose or frequency without consulting your doctor.

Generic and brand names of polyclonal antibodies include:

• Antithymocyte globulin equine
• ATG equine
• Atgam