Antibodies to actin in autoimmune haemolytic anaemia

Actin-reactive antibodies were found in the sera of 95% of all animals tested. The reactivity was species-specific, i.e. reactivity with porcine actin was significantly higher than with rabbit actin. Sera of animals previously immunised with the M. suis adhesion protein MSG1 showed reactivity with actin prior to infection with M. suis indicating that molecular mimicry is involved in the specific autoreactive mechanism. A potentially cross-reactive epitope was detected.This is the first report of autoreactive anti-actin antibodies involved in the pathogenesis of autoimmune haemolytic anaemia.Haemotrophic mycoplasma infections are found in a wide range of domestic and wild animals causing acute haemolytic anaemia or chronic anaemia with immune suppression [1,2]. Generally, they show distinct host specificity. However, there are reports of humans infected with haemotrophic mycoplasmas, i.e. Mycoplasma haemofelis and Mycoplasma suis [3,4]. M. suis causes infectious anaemia in pigs (IAP) [1].Two forms of autoimmune haemolytic anaemia (AIHA) have been described: warm AIHA, which is characterised by autoreactive IgG antibodies binding their target epitope at body temperature [5], and cold AIHA. In cold AIHA, complement-activating autoreactive IgM antibodies bind their antigen, usually the l/i epitope on red blood cells, below body temperature and are strongly agglutinating at 4°C [6,7]. Both types of antibodies occur in 7% of human AIHA cases; this is referred to as mixed AIHA. Sokol and co-workers report only one case of secondary mixed AIHA due to Mycoplasma infection, i.e. M. pneumoniae [8].Mixed AIHA has been found in M. suis-induced IAP. Cold IgM agglutinins targeting glycoproteins on the red blood cells were observed [9,10]. These cold agglutinins occur about four weeks after experimental infection with M. suis. During the acute stage of IAP (clinical attack), acute anaemia, hypoglycaemia and icteroanaemia accompanied by high mortality occur. It is assumed that the s