FAS and Felty syndrome: There are various presumed pathomechanisms for neutropenia (i.e., increased neutrophil consumption in the context of NETosis, Fas-mediated apoptosis, suppression of granulopoiesis by T-LGLs, anti-neutrophil antibodies, anti-G-CSF antibodies), but Felty’s syndrome as well as T-LGL leukemia can sometimes present with pancytopenia, whose causes are less well understood.