Quantification of lymphocytic choriomeningitis virus with an immunological focus assay in 24- or 96-well plates

Titers of lymphocytic choriomeningitis virus (LCMV) were determined on adherent fibroblast cell lines in 24- or 96-well plates. After absorption of virus by cells and 48 h incubation under a methylcellulose overlay, cell monolayers were fixed with 4% formaldehyde in phosphate-buffered saline, permeabilized by incubation in 0.5% Triton X-100 in balanced salt solution and then stained with a monoclonal rat anti-LCMV and aperoxidase-labeled second stage antibody. The sensitivity of the assay is within a factor of 2–4 of conventional plaquing methods. The method also detects poorly or non-plaquing LCMV isolates, and therefore drastically reduces the need for titration of LCMV in mice. The method is quicker (2–3 days), as compared to conventional methods (4–6 days) and less expensive in terms of work and materials.