Two cases of myelodysplastic syndrome with extramedullary polyclonal plasma cell proliferation and autoantibody production: possible role of soluble Fas antigen for production of excessive self-reactive B cells.

Two cases of myelodysplastic syndrome (MDS) with extramedullary polyclonal plasma cell proliferation and autoantibody production are reported. These cases, which showed leukemic change of refractory anemia with excess of blast (RAEB), developed lymph node swelling and muscle abscess; both were infiltrated mainly with plasma cells, without preceding infection. The proliferation of plasma cells was polyclonal and was proven by negative rearrangement of immunoglobulin heavy chain gene or polyclonal staining of immunoglobulin light chains. These patients showed polyclonal gammopathy and autoantibody production such as positive antinuclear factor and direct antiglobulin test. As was observed in one of the present cases, and as we reported previously, the elevated level of soluble Fas antigen in MDS patients, and its inhibition of apoptotic signaling may be responsible for the excessive accumulation of self-reactive B cells, resulting in these clinical manifestations.