Anti-B antibodies are hypothesized to originate from antibodies produced against Gram-negative bacteria, such as E. coli, cross-reacting with the α-D-galactose on the B glycoprotein.However, it is more likely that the force driving evolution of allele diversity is simply negative frequency-dependent selection; cells with rare variants of membrane antigens are more easily distinguished by the immune system from pathogens carrying antigens from other hosts. Thus, individuals possessing rare types are better equipped to detect pathogens. The high within-population diversity observed in human populations would, then, be a consequence of natural selection on individuals. Clinical relevance
The carbohydrate molecules on the surfaces of red blood cells have roles in cell membrane integrity, cell adhesion, membrane transportation of molecules, and acting as receptors for extracellular ligands, and enzymes. ABO antigens are found having similar roles on epithelial cells as well as red blood cells. Bleeding and thrombosis (von Willebrand factor)
The ABO antigen is also expressed on the von Willebrand factor (vWF) glycoprotein, which participates in hemostasis (control of bleeding). In fact, having type O blood predisposes to bleeding, as 30% of the total genetic variation observed in plasma vWF is explained by the effect of the ABO blood group, and individuals with group O blood normally have significantly lower plasma levels of vWF (and Factor VIII) than do non-O individuals.
Operations Enduring Freedom and Operation Iraqi Freedom are some of the most recognizable campaigns as they have to do with the Iraq and a Afghanistan conflicts.<Owens, John, Charles, 2008)>
Battle: this describes a subset of a campaign that will have specific military goals and geographic objectives, as well as clearly defined use of forces, such as the Battle of Gallipoli, which operationally was a combined arms operation originally known as the "Dardanelles landings" as part of the Dardanelles Campaign, where about 480,000 Allied troops took part. Engagement: this describes a tactical combat event or contest for a specific area or objective by actions of distinct units. For example, the Battle of Kursk, also known from its German designation as Operation Citadel, included many separate engagements, several of which were combined into the Battle of Prokhorovka. The Battle of Kursk, in addition to describing the initial German offensive operation, also included two Soviet counter-offensive operations: Operation Kutuzov and Operation Polkovodets Rumyantsev. Strike: this describes a single attack, upon a specified target. This often forms part of a broader engagement. Strikes have an explicit goal, such as rendering facilities such as airports inoperable, assassinating enemy leaders, or limiting the delivery of supplies to enemy troops. Definition
Parallel to and reflecting this framework for operations are organized elements within the armed forces which prepare for and conduct operations at various levels of war.