Editing Humoral immunity (section)

== Antibodies ==
{{main|Antibody}}
[[Antibody|Antibodies]] or Immunoglobulins are [[Glycoprotein|glycoproteins]] found within blood and [[lymph]]. Structurally, antibodies are large Y-shaped [[globular protein]]s. In mammals, there are five types of antibodies: [[immunoglobulin A]], [[immunoglobulin D]], [[immunoglobulin E]], [[immunoglobulin G]], and [[immunoglobulin M]]. Each immunoglobulin class differs in its biological properties and has evolved to deal with different antigens.<ref name="Pier">{{cite book|title=Immunology, Infection, and Immunity|vauthors=Pier GB, Lyczak JB, Wetzler LM|publisher=ASM Press|year=2004|isbn=9781683672111}}</ref> Antibodies are synthesized and secreted by plasma cells that are derived from the B cells of the immune system.

An antibody is used by the acquired immune system to identify and neutralize foreign objects like bacteria and viruses. Each antibody recognizes a specific antigen unique to its target. By binding their specific antigens, antibodies can cause [[Agglutination (biology)|agglutination]] and precipitation of antibody-antigen products, prime for [[phagocytosis]] by [[Macrophage|macrophages]] and other cells, block [[virus|viral]] receptors, and stimulate other immune responses, such as the [[Complement system|complement pathway]].

An incompatible [[blood transfusion]] causes a [[transfusion reaction]], which is mediated by the humoral immune response. This type of reaction, called an acute [[hemolytic]] reaction, results in the rapid destruction (hemolysis) of the donor [[red blood cell]]s by host antibodies. The cause is usually a clerical error, such as the wrong unit of blood being given to the wrong patient. The symptoms are fever and chills, sometimes with back pain and pink or red urine ([[hemoglobinuria]]). The major complication is that [[hemoglobin]] released by the destruction of red blood cells can cause [[acute kidney failure]].