Erythrocyte receptors for Mycoplasma pneumoniae are sialylated oligosaccharides of Ii antigen type

Abstract

Among the pathological effects in man following infection with Mycoplasma pneumoniae is a transient autoimmune disorder characterized by the presence of high-titre erythrocyte auto-antibodies (cold agglutinins)^1,2. These autoantibodies are usually directed against the carbohydrate antigen termed I (ref. 3) which consists of a branched oligosaccharide^4,5. The mechanism by which the anti-I antibodies are elicited is unknown. However, sialic acid-containing receptors have been implicated in the adherence of M. pneumoniae to erythrocytes and other cell types⁶, and both I and the related antigen i occur on erythrocytes in sialylated form⁷: i is the predominant antigen on fetal erythrocytes and I is predominant in adults⁸. Anti-I antibodies might arise in M. pneumoniae infection in response to a modification of the ‘self’ antigen-I as a result of its interaction with this agent^9,10. Here we report our study of the specificity of the interaction of M. pneumoniae with human erythrocytes. We found that this interaction is mediated by long chain oligosaccharides of sialic acid joined by α2–3 linkage to the terminal galactose residues of poly-N-acetyllactosamine sequences of Ii antigen type.