Characterization of plasma cell populations at autopsy after human allogeneic bone marrow transplantation.

Postmortem fixed tissue sections of the lymphoid and digestive systems of eight consecutive leukemic patients dying of various diseases after bone marrow transplantation (BMT) were analyzed for the presence of the heavy chains gamma, alpha, mu, delta, and epsilon and light chains kappa and lambda, with the use of a standard immunoperoxidase method. Two distinct types of plasma cell populations were found. The first type was a widely distributed polyclonal plasma cell population, lacking IgD-positive plasma cells and germinal centers. The second type of plasma cell population, found in 6 of 8 patients, was a group of monoclonal plasma cell populations positive for the heavy chains gamma, alpha, mu, or delta. Recent immunohistologic observations of the human lymph node suggest that the first type of polyclonal plasma cell population could arise from a nonspecific expansion of sIgM+, sIgD- B lymphocytes. The lack of germinal centers, a structure closely involved in specific-antibody production, may correlate with the poor specific-antibody response documented in patients after BMT. The monoclonal plasma cell populations, found with an unexpectedly high frequency, are probably related to a functional T-cell defect.