|Human blood is divided into four major different types: A, B, Ab, and O. The differences are due to antigens present on the surface of the blood cells. Antigens are substances that produce an immune reaction by their nature of being perceived as foreign to the body. In response, the body produces substances called antibodies that nullify or neutralize the antigens. In blood, these antigens are called agglutinogens because their presence can cause the blood to clot. An individual with type AB blood is a universal recipient, and an individual with type O blood is a universal donor.
Scholarly peer review is the process of subjecting an author's scholarly work, research, or ideas to the scrutiny of others who are experts in the same field, before a paper describing this work is published in a journal. The work may be accepted, considered acceptable with revisions, or rejected. Peer review requires a community of experts in a given (narrowly defined) field, who are qualified and able to perform reasonably impartial review.