Ultrastructural analysis of peripheral blood mononuclear cells in renal allograft recipients

Renal transplanted patients receiving immunosuppressive therapy with glucocorticoids (GC) and azathioprine show in the peripheral blood numerous large mononuclear cells. The origin and the lineage of these cells was not clearly established. In the present study we investigated the surface phenotype and the ultrastructural characteristics of this subset constituted by large mononuclear cells. From peripheral blood mononuclear cells (PBL) of allograft recipients, a cell preparation exhaustively depleted of the relatively numerous monocytes was obtained. At ultrastructural examination two main cellular populations were distinguished: the predominant one (congruent to 85%) was constituted by cells with lymphoid morphology while the other (congruent to 15%) showed myeloid appearance. The large lymphoid cells, T4 or T8 positive, did not express Ia molecules on the surface and were morphologically suggestive of cells in an intermediate stage of the cell cycle between resting and activated lymphocytes. The myeloid population was constituted by promyelocytes, myelocytes and metamyelocytes. Promyelocytes and myelocytes capable of cell division are responsible for the increase of 3H-thymidine incorporation observed in transplanted patient PBL. In conclusion our data suggest that in allograft recipients the immunosuppressive therapy with GC and azathioprine may inhibit the lymphocyte blast transformation and can influence the release of immature myeloid cells responsible for the PBL increased 3H-thymidine incorporation.