The expression of blood group P1 in post-enteropathic haemolytic uraemic syndrome.

Blood group P1 expression was scored by direct agglutination in 32 patients who had previously developed post-enteropathic haemolytic uraemic syndrome (HUS). Sixty-six children of similar ages undergoing venepuncture for other renal disorders acted as controls. The expression of P1 in controls was that expected from the normal caucasian population, 23% being negative. By contrast, there was an excess of HUS patients with weak or absent expression of P1 (chi 2 for linear trend 5.45, P less than 0.02), and this was particularly evident in those with a poor outcome. Verotoxin (VT), which is associated with HUS, requires the terminal disaccharide of the P1 antigen to bind to cells, and after internalization disrupts the transcription of ribonucleic acid. Mature erythrocytes do not synthesize protein and may be toxin resistant. We postulate that strong expression of P1 antigen may promote the binding of VT to red cells and thus reduce the dose to vulnerable nucleated endothelial cells. P1 positivity may be protective, and P1 negativity a risk factor in HUS.