To measure the cytotoxicity of TNF present in sera samples,
a standard assay with L929 cells, a fibroblast continuous cell line,
was used as described previously by Ruff and Gifford (1980). The
percentage cytotoxicity was calculated as follows: (AcontrolAsample/
Acontrol) 100. Titres were calculated as the reciprocal of the dilution
of the sample in which 50% of the cells in the monolayers were
lysed. TNF activity is expressed as pg/mL estimated from the ratio
of a 50% cytotoxic dose of the test to that of standard mouse
recombinant TNF.