Expression of the paired receptors CEACAM1 and CEACAM28 in stimulated T cells. RNA was isolated from purified lymphocyte populations. CEACAM1 and CEACAM28 transcripts were identified by RT-PCR. Gene-specific primers located in the N domain and transmembrane exons were used for CEACAM1 cDNA amplification. The primers for CEACAM28 cDNA detection coamplified CEACAM30 cDNA due the close relatedness of the two genes. For comparison, GAPDH cDNA (226 bp) was amplified from the same cDNA samples. (A) Activation of T cells was controlled by determining blast formation by flow cytometry. Blast formation characterized by cell enlargement is demonstrated by an increase of the forward scatter of the T cells (encircled cell populations) (B) The products were separated by agarose gel electrophoresis in the presence of ethidium bromide and visualized by UV illumination. The amount of cDNA was quantified by endpoint determination with the Quantity 1® software. Note the increase of the CEACAM1/CEACAM28 cDNA ratio after stimulation of T cells with IL-2 and CD3 (C).