Effect of HLA class II molecule signaling on the expression of FasL mRNA. Human splenic B lymphocytes were stimulated as indicated for 4 hours. RT-PCR amplification was performed, and PCR products were visualized after electrophoresis in a 2% agarose gel (a). The autoradiograph was subsequently analyzed with a densitometer, which was normalized by dividing the FasL PCR product with the density of the GAPDH profile (b). The PCR product of FasL amplification migrated at the predicted size of 510 bp. Lane 1, nonstimulated; lane 2, 6.7 μg/mL anti–HLA class II MoAb (L227 XL); lane 3, bacterial superantigen TSST-1; lane 4, PMA and ionomycin.