FIG. 1.

Induction of LPS tolerance in human Mono Mac 6 cells. Mono Mac 6 cells were precultured for 48 h with or without LPS (20 ng/ml), washed, and stimulated with or without LPS at 1 μg/ml for 1 h (for mRNA determination) or for 6 h (for protein analysis). Isolated RNA was reverse transcribed and amplified for α-enolase (32 cycles) and for TNF (34 cycles). Densitometry values for TNF, corrected for enolase prevalence, were 17.8, 48.7, 9.1, and 17.4% for lanes 1 to 4. In an average of four experiments, −/+ cells (A, lane 2) gave a value of 58.4 ± 16.9%, while for +/+ cells (lane 4) the value was 26.2 ± 15.0% (P < 0.01). Assay of supernatants from the same experiment for TNF protein in the WEHI 164/actinomycin D bioassay (B) gave values of <5 U/ml for all cultures except the LPS-stimulated naive cells in lane 2, which produced 52.2 U/ml. In an average of four experiments, −/+ cells (lane 2) gave 132.7 ± 58.3 U/ml and +/+ cells (lane 4) gave 9.8 ± 6.1 U/ml (P < 0.01).