A simple assay based on HIV infection preventing the reclustering of MT-4 cells

This report confirms and extends the recent work of Pauwels et al. on a "reclustering" assay (a simple microtitration plate method) for the determination of human immuno-deficiency virus (HIV) infection of MT-4 cells. MT-4 cells, which are highly susceptible to and permissive for HIV, typically grow in clusters. In the absence of virus these cell aggregates, after dissociation by pipetting, reform into clusters within 2 to 3 hours. Growth of HIV results in an inhibition of reclustering, with an end-point some 4-5 days after initiation of infection. In cultures inoculated with 5 to 8 TCID(50) of HIV, only 2-4% of the cells remain viable after 4 days. Correspondingly, HIV antigens can be detected by immunofluorescence in more than 90% of the cells remaining in the culture. The sensitivity of the "reclustering" assay is only slightly less than that of the immunofluorescence test. A colorimetric assay is also described that employs a tetrazolium salt (designated as MTT) to measure the cytolytic effect of various dilutions of HIV; comparable virus titres were obtained. This reclustering assay now appears to offer the simplest method for titration of prototype HIV in virus stocks and when used in drug evaluation tests and for measurement of HIV neutralizing antibodies.