Expression of restricted immunoglobulin isotypes in plasmacellular hyperplasia after allogeneic bone marrow transplantation.

Plasmacellular hyperplasia in lymphoid tissue was found in 4 out of 9 patients 1-6 months after allogeneic bone marrow transplantation as treatment for leukaemia. In the plasma cell populations, 13-85% expressed a single immunoglobulin light and heavy chain isotype (monotypic Ig expression). DNA analysis, using a DNA probe specific for heavy chain JH gene segments and for light chains, did not reveal the presence of clonally restricted B lymphocytes. The patients' sera lacked homogeneous immunoglobulins. We conclude that plasmacellular hyperplasia found after allogeneic bone marrow transplantation represents a polyclonal B-cell expansion- with a restriction in Ig isotype.