Expression of CIITA-specific mRNA in the human B- and T-cell lines analyzed in this study. Semiquantitative RT-PCR analysis of mRNA purified from equivalent number of cells was performed. Quantification of specific transcripts was carried out by densitometry, and values were expressed as relative amount of transcripts in the abscissa, assuming as reference unit value the one measured in the Raji cells. RJ/CIITA and M4/CIITA indicate RJ2.2.5 and MOLT-4 cells, respectively, stably transfected with CIITA.