Blood type 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. ABO IgM antibodies are produced in the first years of life by sensitization to environmental substances such as food, bacteria, and viruses. 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
Jehovah's Witnesses and blood transfusions their comments into English reads: According to sociologist Richard Singelenbreg, the statement appearing in the Dutch edition of "Consolation" may have been published without knowledge of the doctrinal position published in the English July 1945 issue of "Consolation" by the Watch Tower Society's headquarters in the United States. In 1945, the application of the doctrine on blood was expanded to prohibit blood transfusions of whole blood, whether allogeneic or autologous. The prohibition did not specify any punitive measures for accepting a transfusion, but by January 1961—in what was later described as an application of "increased strictness"—it was ruled that it