Induction of autoimmune diseases by radiation exposure. Changes in molecular structures of neutrophil myeloperoxidase

It has been suggested that functional abnormalities of leucocyte induced by radiation exposure might be related to development of autoimmune diseases. The authors demonstrated that fragmentation of MPO, a lysozyme enzyme of neutrophil caused by high dose exposure resulted in a lowering of its activity and an enhancement of its degradation. It was assumed that release of MPO fragment, 30 kDa might be involved in development of autoimmune diseases. In this study, 4 peptides in neutrophil; defensin 3, hCAP-18, FMLP-R and CD35 were selected as the indicators for activation of neutrophils and the effects of γ-ray exposure on their mRNA expressions were investigated. A suspension of neutrophils from healthy peripheral blood were exposed to γ-ray at 0, 10 or 30 Gy and incubated after addition of cytochalasin B and FMLP for 10 min to release MPO. The activities of MPO in the cell and in the extracellular fluid were assayed with tetramethylbenzidine as the substrate. The MPO activity released from the neutrophils was significantly increased by γ-ray exposure at 10 or 30 Gy. The increase was slightly higher for exposure at 10 Gy than that at 30 Gy. Next, the effects of exposure were investigated on mRNA expressions of 4 different peptides of neutrophil. From the exposed cells, whole RNA were extracted by AGPC method and used as a primer to produce the respective cDNAs and mRNA assay was conducted by PCR method. The exposure to γ-ray at 10 Gy increased mRNA expressions of all four peptides. The increase was marked for CD35, moderate for defensin 3 and hCAP-18, and slight for FMLP-R. These results indicate that MPO fragments can be produced through radiation exposure as well as heat treatment. Therefore, it was suggested that anti-MPO antibody, MPO-ANCA might be produced by MPO fragments produced by radiation and/or lymphatic functional disorders. (M.N.)