PCR detectable Y chromosome-specific DNA but no intact Y chromosome-bearing cells in polymyositis biopsies of two women with male offspring.

Aims: Pregnancy-related and idiopathic adult polymyositis are inflammatory myopathies of unknown aetiology in which CD8 positive T cells are found in close association with the up-regulation of human leukocyte antigen (HLA) class I on affected muscle cells. A similar polymyositis can also occur in patients with chronic graft versus host disease, wherein graft lymphocytes may be involved in the myositis. We investigated whether polymyositis that was temporally related to pregnancy, contained Y chromosome-bearing cells or signals using polymerase chain reaction (PCR) in biopsies of lesional muscle from two women who had given birth to sons. Furthermore, if Y chromosome material was present, we investigated whether it was contained in the intact inflammatory cells (CD8 positive lymphocytes for example), fetal macrophages, or differentiated fetal stem cells engrafted in the lesional skeletal muscle, and thus whether fetal cells played a role in the pathogenesis of the myositis.

Methods: PCR analysis was used for the Y chromosome in lesional tissue and fluorescence in situ hybridisation (FISH) for intact cells carrying the Y chromosome.

Results: Small amounts of Y chromosome material were detected on second round PCR in fresh frozen tissue. No Y chromosome-bearing intact cells of lymphocytic, macrophage or muscle lineage were detected.

Conclusion: Our results suggest that microchimeric fetal cells are not found in the lesional tissue of pregnancy-related polymyositis.