Human sera , old world monkeys and primates contain unique anti- Gal antibody directed against an epitope Gala1 - 3Galb1 - 4GlcNAc (a- gal ) . Antibodies with such specificity are the most common antibodies in the sera of a group of species. The anti- Gal are involved in a number of processes related to the defense of the organism , but they may also be involved in the pathogenesis of certain diseases.