Cell-mediated suppression of megakaryocytopoiesis in acquired
amegakaryocytic thrombocytopenic purpura
AM Gewirtz, MK Sacchetti, R Bien and WE Barry
Acquired amegakaryocytic thrombocytopenic purpura (AATP) is a disorder of
hematopoiesis characterized by severe thrombocytopenia due to a selective
reduction or total absence of megakaryocytes in an otherwise
normal-appearing bone marrow. Although the development of autoantibodies
directed against cells in the megakaryocyte progenitor cell pool has been
implicated in the pathogenesis of this disorder, cell-mediated suppression
of megakaryocytopoiesis has not been described. Accordingly, we report two
cases of AATP in which in vitro suppression of megakaryocyte colony
formation by autologous ancillary marrow cells was demonstrable.
Light-density bone marrow mononuclear cells (MNCs) obtained from both
patients were either plated directly into plasma clot cultures, or after
first being depleted by adherent monocytes (M phi) or T lymphocytes using
standard methodologies. In some experiments, the depleted ancillary marrow
cells were recovered for autologous co-culture studies with the MNCs from
which they had been depleted. Megakaryocyte colony formation was detected
in the cultures using an indirect immunofluorescence assay with a rabbit
anti- human platelet glycoprotein antiserum. Removal of M phi (n = 6), or T
lymphocytes (n = 4) from normal marrow MNCs had no apparent effect on
colony formation. In contrast, depleting T lymphocytes from the MNCs of
patient 1 significantly augmented megakaryocyte colony formation; a similar
effect was observed after depleting M phi from the MNCs of patient 2. This
observed augmentation in colony formation could be abrogated by autologous
co-culture with the putative suppressor cell at effector cell/target cell
ratios of 1:10 in the case of T lymphocytes or 1:5 in the case of M phi.
Neither suppression nor stimulation of megakaryocyte colony formation was
observed after culturing normal MNCs with autologous T cells (n = 4) or M
phi (n = 3) at similar or greater ratios. We also observed inhibition of
megakaryocyte colony formation after culturing normal MNCs in the presence
of tissue culture medium conditioned by the M phi of patient 2. This effect
was shown to be specific for megakaryocytes since this same conditioned
medium had no significant effect on BFU-E and CFU-E-derived colony
formation by autologous marrow mononuclear cells. These results suggest
that: both T cells and M phi are capable of exerting a regulatory effect on
the proliferation of human megakaryocyte progenitor cells (CFU-Meg); in the
case of M phi, a soluble factor elaborated by these cells may be
responsible for suppressing CFU-Meg growth; and aberrant ancillary cell-
megakaryocyte progenitor cell interactions may lead to clinically
significant disease.
Volume 68,
Issue 3,
pp. 619-626,
09/01/1986
Copyright © 1986 by The American Society of Hematology
