Plasmacellular hyperplasia after allogeneic bone marrow transplantation.

B lymphoid cells with monotypic immunoglobulin (Ig) expression, i.e., a single Ig heavy chain isotype combined with a single light chain type, were observed in five of nine patients after allogeneic bone marrow transplantation. Three patients exhibited plasmacellular hyperplasia of lymph nodes and spleen; in one case the monotypic cells were immunoblasts in a lymph node, and one patient suffered from an immunoblastic lymphoma along the gastrointestinal tract. We present the clinical history and the detailed (immuno) histologic analysis of lymphoid tissue from three patients. In DNA analysis of lymph node using DNA probes specific for the JH-gene segment of Ig heavy chains and for light chains, bands indicative of single Ig gene rearrangements were not observed. Thus, the monotypic B lymphoid elements represent polyclonal B cell expansion.