Qa-2 siRNA reduced Qa-2 mRNA and the frequency of Qa-2 positive cells in PBMC of normal mice. PBMC isolated from mice were transfected with Qa-2 siRNAs with different Qa-2 domains for 24 hrs, and the expression of Qa-2 was then determined by reverse transcriptase-PCR and FACS analysis. Lanes 4, 5 and 6 (α3 domain, transmembrane domain, and cytoplasmic domain, respectively) showed that siRNA effectively reduced the Qa-2 mRNA levels. Lane 3 (leader peptide) did not decrease the Qa-2 level. Lane 7 (a mixture of leader peptide, α3 domain, transmembrane domain, and cytoplasmic domain) also did not decrease the Qa-2 level. Lane 1, control (not treated); Lane 2, 5% glucose treated; Lane 3, leader peptide 200 nmole; Lane 4, α3 domain 200 nmole; Lane 5, transmembrane domain 200 nmole; Lane 6, cytoplasmic domain 200 nmole; Lane 7, mixed 200 nmole (leader peptide + α3 domain+ transmembrane domain + cytoplasmic domain).