Regarding the antigen property of the blood all human beings can be classified into four groups, those with antigen A (group A), those with antigen B (group B), those with both antigen A and B (group AB) and those with neither antigen (group O). The antibodies present together with the antigens are found as follows:
Antigen A with antibody B
Antigen B with antibody A
Antigen AB with neither antibody A nor B
Antigen null (group O) with both antibody A and BThere is an agglutination reaction between similar antigen and antibody (for example, antigen A agglutinates the antibody A and antigen B agglutinates the antibody B). Thus, transfusion can be considered safe as long as the serum of the recipient does not contain antibodies for the blood cell antigens of the donor.The ABO system is the most important blood-group system in human-blood transfusion. The associated anti-A and anti-B antibodies are usually immunoglobulin M, abbreviated IgM, antibodies. It has been hypothesized that ABO IgM antibodies are produced in the first years of life by sensitization to environmental substances such as food, bacteria, and viruses, although blood group compatibility rules are applied to newborn and infants as a matter of practice. The original terminology used by Karl Landsteiner in 1901 for the classification was A/B/C; in later publications "C" became "O". Type O is often called 0 (zero, or null) in other languages. Rh blood group system
The Rh system (Rh meaning Rhesus) is the second most significant blood-group system in human-blood transfusion with currently 50 antigens.
Blood Transfusion in Clinical Medicine (10th ed.). Oxford UK: Blackwell Science. ISBN 0-86542-881-6. External links

BGMUT Blood Group Antigen Gene Mutation Database at NCBI, NIH has details of genes and proteins, and variations thereof, that are responsible for blood types
Online Mendelian Inheritance in Man (OMIM): ABO Glycosyltransferase; ABO - 110300
Online Mendelian Inheritance in Man (OMIM): Rhesus Blood Group, D Antigen; RHD - 111680
"Blood group test". Gentest.ch GmbH. Archived from the original on 2017-03-24. Retrieved 2017-03-23. "Blood Facts – Rare Traits". LifeShare Blood Centers. Archived from the original on September 26, 2006. Retrieved September 15, 2006. "Modern Human Variation: Distribution of Blood Types". Dr. Dennis ONeil, Behavioral Sciences Department, Palomar College, San Marcos, California. 2001-06-06. Archived from the original on 2001-06-06. Retrieved November 23, 2006. "Racial and Ethnic Distribution of ABO Blood Types – BloodBook.com, Blood Information for Life". bloodbook.com. Archived from the original on 2010-03-04. Retrieved September 15, 2006. "Molecular Genetic Basis of ABO". Retrieved July 31, 2008.