The detection of defective interfering Rubella virions by a modified hemadsorption technique.

Rubella virus (RV) has been titrated in murine fibroblasts in monolayer cultures using a modified hemadsorption assay. Infected monolayers were incubated in the presence of sheep erythrocytes for 24 h: after the tissue culture slides were washed, the hemadsorption foci were clearly visible on microscopic examination. When serial doubling dilutions of virus suspensions were assayed in this way the decline in the number of hemadsorbing units was proportional to the fractional power of the concn. These data suggest that this simple titration of Rubella virus may be useful in the detection of defective interfering (DI) virions in Rubella populations. The detection of DI Rubella virions by more time-consuming and expensive techniques including isopycnic centrifugation, ribonucleic acid extraction, 125I-labelling, polyacrylamide slab gel electrophoresis, and autoradiography have been described. The clinical importance of defective virions and the need for an inexpensive, rapid means of detecting them are discussed.