Exposure of p19 matrix protein of human T-cell leukemia virus type I (HTLV-I) on the surface of MOLT-4#8 cells after virus adsorption.

The p19 matrix (MA) protein of human T-cell leukemia virus type I (HTLV-I) was exposed on the surface of MOLT-4#8 cells in the very early step of the virus infection. Transfer of the virus-binding MOLT-4#8 cells from 4 degrees C to 37 degrees C resulted in increased detection of the viral gp46 and p19 MA protein on the cells, which was, however, inhibited by 4 degrees C or cytochalasin B treatment. These data showed that increased temperature and fluidity of the cell membrane were required for the increased detection of gp46 and p19 after viral adsorption. On the other hand, exposure of the p19 MA protein was not observed on the virus-treated U937 cells although gp46 was detected. This was not due to inefficient binding of the HTLV-I to the U937 cells, since the methanol-fixed cells were p19 MA protein-positive. MOLT-4#8 cells induced marked cell fusion when co-cultured with MT-2 cells, but U937 cells induced no fusion. All of these results indicated that these two cell lines differed in the property of plasma membrane in terms of degradation of HTLV-I envelope after viral adsorption. Uncoating of the HTLV-I might occur on the plasma membrane, especially on MOLT-4#8 cells.