RESUMO
Transmembrane TNF-? is an integral protein expressed on the surface of avtivated monocytes/macrophages. In order to define the interrelation between TM-TNF and biomembrane, we used an in vitro translation system and microsomal membranes to engender expression models of two types of TM-TNF; TM-TNF anchored to microsomes and naked 26kD TNF without membranes. When the cytotoxic activity of these two types of TNF was compared, the synthesized 26kD TNF was found to exert its effects only in the presence of microsomal membranes. With the use of indirect immunofluorescence technique, we further studied the binding of the in vitro translated 26kD TNF with TNFR on the membrane of HL60 cells. It was found that only TM-TNF attached to the microsomes could bind effectively with TNFR, while naked 26kD TNF could not. These results suggest that binding with biomembrane may be the prerequisite for 26kD TNF to fold properly for displaying its biological effects. In case 26kD TNF is freed from membrane, it can no more bind with TNFR, there by leading to loss of its cytotoxic effect.