title: HLA class I expression on erythrocytes and platelets from patients with systemic lupus erythematosus, rheumatoid arthritis and from normal subjects.
abstract: It has previously been shown, by a haemagglutination assay, that patients with systemic lupus erythematosus (SLE) express increased levels of HLA class I on erythrocytes compared with normal subjects and patients with rheumatoid arthritis (RA). A radioligand-binding assay, using monoclonal antibody W6/32, was devised to quantify HLA class I expression on erythrocytes and platelets. An increased number of class I molecules was expressed on erythrocytes from 45 patients with SLE (mean = 354 molecules per cell, median = 255 molecules, range = 30-1270 molecules per cell), compared with cells from 46 normal subjects (mean = 132, median = 78, range = 40-550) and 31 RA patients (mean = 132, median = 89, range = 26-497). The presence of HLA-B7 correlated with increased class I expression on erythrocytes from both normal subjects and patients with SLE. Levels of HLA class I in serum were measured. All subjects with HLA-A9 (A23, 24) showed higher levels of serum class I than their A9-negative counterparts, and there was no difference in levels between SLE patients and normal subjects. There were no correlations between class I levels in serum and on erythrocytes amongst SLE patients or normal subjects. Red cells were fractionated, according to their age in vivo, on Percoll gradients. Class I levels fell with increasing erythrocyte age in all individuals, but were higher in all fractions from SLE patients compared with age-matched fractions from normal subjects. HLA-B7-positive erythrocytes also expressed higher class I levels in each Percoll fraction, compared with their HLA-B7-negative counterparts, suggesting that enhanced B7 expression is not due to greater structural stability of this class I allotype. These data are compatible with the hypothesis that class I is expressed as an intrinsic protein of erythrocyte membranes and that expression is increased amongst patients with SLE.
authors.affiliation: Department of Medicine, Royal Postgraduate Medical School, Hammersmith Hospital, London.
authors.forename: M
authors.initials: M
authors.lastname: Botto
authors.forename: A K
authors.initials: AK
authors.lastname: So
authors.forename: C M
authors.initials: CM
authors.lastname: Giles
authors.forename: P D
authors.initials: PD
authors.lastname: Mason
authors.forename: M J
authors.initials: MJ
authors.lastname: Walport
mesh_terms: D001172:Arthritis, Rheumatoid / Q000276:immunology*; D001792:Blood Platelets / Q000276:immunology*; D004912:Erythrocytes / Q000276:immunology*; D015234:HLA-A Antigens / Q000032:analysis; D015793:HLA-B7 Antigen / Q000032:analysis; D015395:Histocompatibility Antigens Class I / Q000032:analysis*; D006801:Humans; D008180:Lupus Erythematosus, Systemic / Q000276:immunology*
chemical_list: D015234:HLA-A Antigens; C037709:HLA-A9 antigen; D015793:HLA-B7 Antigen; D015395:Histocompatibility Antigens Class I