Growth-stimulating activity toward HEL cells on coculture with HESS-5 cells with direct cell contact of the anti-sense PON of CD18 (integrin β2 chain). HEL cells were cultured in RPMI-1640 medium supplemented with 0.1% (wt/vol) BSA, and an antisense (CD18/AS; positions 1-24), sense (CD18/S; positions 1-24), or random (CD18/RS) PON at a final concentration of 2 μmol/L (□) or 5 μmol (▪). After 24 hours of incubation, the HEL cells were harvested and subjected to proteinase treatment for digestion of the cell surface CD18 molecules. After the treatment, the HEL cells were cocultured with a confluent layer of HESS-5 cells at the concentration of 5 × 10³ cells/well of a 96-well cell culture plate in 200 μL of RPMI-1640 medium supplemented with 0.1% BSA and 2 or 5 μmol/L PONs. After 2 days in culture, the ³H-thymidine incorporation assay described under Materials and Methods was performed. The results are expressed as mean values ± SD of the mean.