Abnormalities of membrane protein composition in patients with autoimmune haemolytic anaemia.

Abstract

Acquired abnormalities of red cell membrane protein composition in 37 patients with a positive direct antiglobulin test have been studied: 17 patients had true autoimmune haemolytic anaemia and 20 were HIV-infected subjects with a positive direct antiglobulin test but without signs of haemolysis. The study was carried out by performing sodium dodecyl sulphate polyacrylamide gel electrophoresis of ghost proteins followed by densitometric evaluation of the areas under the peaks, normalized by the total (alpha + beta) spectrin content. Results show a significant decrease of bands 3, 4.1 and 4.2 over spectrin in patients with autoimmune haemolysis as compared to controls; at least in a small subset of patients, different specificities recognized by autoantibodies do not seem to account for these abnormalities which are reproducible independently from the molecular size of bands immunoprecipitated by autoantibodies. A similar decrease of protein 4.2 but not of band 3 staining intensity is also noticeable in HIV patients with a positive direct antiglobulin test. These results are consistent with the hypothesis that, following interactions between autoantibodies and autoantigens, modifications occur on membrane proteins resembling a variety of quantitative defects described in inherited haemolytic anaemias, and mainly the "vertical interaction defects' of hereditary spherocytosis. Moreover, the decrease of band 3 staining intensity seems to represent a feature of patients with immune mediated haemolysis and not only with autoantibody binding.