Based on the serologic similarities, Rh factor was later also used for antigens, and anti-Rh for antibodies, found in humans such as those previously described by Levine and Stetson. Although differences between these two sera were shown already in 1942 and clearly demonstrated in 1963, the already widely used term "Rh" was kept for the clinically described human antibodies which are different from the ones related to the rhesus monkey. This real factor found in rhesus macaque was classified in the Landsteiner-Wiener antigen system (antigen LW, antibody anti-LW) in honor of the discoverers.[9][10]