Lowered susceptibility of K-562 cells treated with gamma interferon in serum-free medium to natural killer cell-mediated cytolysis

: K-562 cells grown in serum-free medium were treated with gamma interferon (IFN-gamma) and they became significantly less susceptible to natural killer (NK) cell-mediated cytolysis. To examine if this loss in susceptibility was related to induced differentiation events, the presence of various antigens was determined after induction. There was a coincident expression of class I HLA common antigen, although it is not clear if this is a direct causal relationship. The level of the constitutively expressed myelomonocytic antigen, reactive with anti-Leu-M1, was not affected by IFN-gamma induction and three normally nonexpressed monocytic antigens, defined by monoclonal antibodies, remained unexpressed. IFN-gamma did induce an enhanced expression of IL-2 receptors on K-562 cells after 2 days of treatment but, thereafter, the expression appeared to be suppressed. Electron microscopy of IFN-gamma-treated cells revealed the development of increased surface blebbing and electron-dense cytoplasmic inclusions. These ultramicroscopic changes could not be correlated with definitive differentiation events. We suggest that IFN-gamma treatment of K-562 cells induces class I HLA expression and morphological changes that may be important to differentiation events that render the cells less susceptible ot NK-mediated cytolysis.