High inducibility of heat shock protein 72 (hsp72) in peripheral blood mononuclear cells of aplastic anaemia patients: a reliable marker of immune‐mediated aplastic anaemia responsive to cyclosporine therapy

To better characterize immunologic aberrations in aplastic anaemia (AA), we examined peripheral blood mononuclear cells (PBMC) of 67 patients with AA and other patients with various haematological diseases for the expression of heat shock protein 72 (hsp72), which is inducible in lymphocytes by various stressors including antigenic stimulation. When freshly obtained PBMC were examined using flow cytometry, the proportion of cells expressing hsp72 in cytoplasm was significantly higher in allogeneic marrow transplant recipients (22 ± 15%, mean ±standard deviation (SD)) and AA patients (17 ± 21%) than in normal individuals (6 ± 3%). When PBMC were tested after heat treatment, only the proportion of hsp72+ cells of AA patients (37 ± 30%) was significantly higher than that of the normal control (17 ± 11%). Dual fluorescence analysis of the PBMC revealed that the majority of hsp72+ cells was CD3+. For 28 untreated AA patients, the proportion of hsp72+ cells in those who later responded to cyclosporine (CyA) (62 ± 24%) was higher than that in non‐responders (19 ± 13%). Immunoblotting analysis revealed predominant expression of hsp72 in T cells. These findings indicate that high inducibility of hsp72 in PBMC by heat treatment is an immunologic aberration characteristic of CyA‐responsive AA and that this simple test may be useful for identifying a subset of AA patients responsive to immunosuppressive therapy.