Characterisation of T-helper cell subsets in human autoimmune haemolytic anaemia
Autoimmune haemolytic anaemia provides an opportunity to characterise the T-cell response to an autoantigen of known pathological relevance. In most cases, AIHA is characterised by the production of autoantibodies to the Rh proteins. The aims of this work were to confirm that human AIHA is T-helper cell dependent and whether specific immunotherapy could be developed to target the T-helper cell response. Peripheral blood mononuclear cells (PBMC) were isolated from patients with either primary AIHA and stimulated in vitro with a panel of 42 15-mer peptides with 5 mer overlaps spanning the entire sequence of the RhD and CE proteins. PBMC with 22/27 patients proliferate in response to stimulation with at least one of these peptides compared to only 4/14 healthy donors. The proliferating cells were identified as T-helper cells by flow cytometry analysis and abrogation of the response using MHC class II blocking antibodies. There is a predominance of HLA-DRB*1501 and HLA-DQB*06 haplotypes whilst the HLA-DRB1*07 haplotype is under represented amongst the panel of primary AIHA patients. Antibodies directed against HLA-DR and HLA-DQ can inhibit the T-cell response to peptides from the Rh proteins (anti-HLA-DR>anti-HLA-DQ) suggesting that these MHC class I molecules play an important role in presenting the synthetic Rh peptides. The pathogenic T-helper cell response to RhD protein in vivo, may depend upon the balance of pathogenic and regulatory epitopes that are processed and presented by antigen presenting cells.