Electron-microscopic identification of infectious particles of lymphocytic choriomeningitis.

LCM virus, strain WE--grown on L cells--and labeled with 3H-uridine was centrifuged to equilibrium in a sucrose density gradient and examined in fractions for infectivity, incorporated radioactivity, and electron-microscopic features. The peak of infectivity is congruent with the one of radioactivity (density = 1.17 g/ml). LCM virus specificity of the radioactive peak was proved by precipitation of the radioactivity with anti-LCM virus antiserum. The peak fractions showed an abundance of 106 +/- 14 nm (1s) particles. They could be agglutinated with specific anti-LCM virus antiserum but not with antiserum directed against the histocompatibility (H-2) antigens of L cells.