Anti-Streptolysin O Antibody (ASO)

Anti-streptolysin O (ASO or ASLO) is the antibody produced against an antigen produced by Lancefield group A streptococci. The enzyme is called streptolysin O, wherein the O stands for oxygen-labile; the other antigen being oxygen stable streptolysin-S. Both the enzymes are involved in producing hemolysis, i.e., digestion of blood, in particular, beta-hemolysis. When the body is infected with streptococci, it produces antibodies against the various antigens that the streptococci produce. ASO is one such antibody. So, a raised or rising levels can indicate past or present infection. Historically was one of the first bacterial markers used for diagnosis and follow up of rheumatism or scarlet fever. Its importance in this regard has not diminished.These antibodies produced against the bacteria cross react with human antigens (mainly collagen) and hence attack the cellular matrix of various organs, mainly the heart, joints, skin, brain, etc.