270 The Lymphocyte and Lymphocytic Tissue 



Metastatic nonreticular sarcoma cells may simulate reticular malignancy 

 even more closely. In one such case that we have studied, the diagnosis 

 of primary pleomorphic reticulum cell sarcoma was finally rejected only 

 because of the demonstration of imprinted strap cells bearing the unmistak- 

 able cross-striations of the parent rhabdomyosarcoma. 



BLOOD-FORMING RETICULUM CELLS 



In the forego i no- we have described the cellular changes in some of the 

 more important conditions affecting the reticulum cell as a reticulum cell or 



Fig. 19-7. Hematopoietic reticulum cell [center) from a lymph node 

 imprint in infectious mononucleosis. Compare with inactive reticulum 

 cell of Fig. 1<)-1 and reactive reticulum cell of Fig. l!>-2. Leishman 

 stain. (X 1100) 



affecting the macrophage to which it is capable of transforming. Heterol- 

 ogous lymphocyte formation by the reticulum cell (RE cell, mesenchymal 

 cell, histiocyte) is also designated as heterologous lymphocytopoiesis. It con- 

 sists of a change from the relatively inactive-appearing tissue RE cell (Fig. 

 19-1 1) to a free, active, blood-forming RE cell (Figs. 19-7, 19-8) and only then 

 to the Iymphoblast (Fig. 19-11). Most flow sheets derive the lymphoblast 

 directly from the RE cell (stromal connective tissue cell), omitting reference 

 to, and discussion of, some necessary intermediate (blood-forming RE cell) 

 as the smaller, inactive RE cell nucleus becomes larger and changes from 

 the coarser connective tissue nuclear pattern to the finer stipple or network 



