Mature moDCs are more resistant than immature moDCs to HCMV-induced down-regulation of surface MHC and costimulatory epitopes, and they secrete a transferable factor(s) that inhibits DC-stimulated T-cell responses. (A) Percent fluorescent intensity of HCMV-exposed relative to non-HCMV-exposed moDCs (100%). HCMV-infected, IE1-positive immature moDCs down-regulated class I and II MHC, CD86, and CD80 expression, whereas bystander, uninfected, IE1-negative cells from the same HCMV-exposed cultures up-regulated these epitopes (top). Unlike immature moDCs, however, HCMV exposure only slightly affected the phenotype of mature moDCs (bottom). The differences between IE1-positive and IE1-negative cells were much less in mature than in immature moDC cultures exposed to HCMV, with the exception that infected IE1-positive cells markedly down-regulated surface CD83 (bottom). (B) Virus-free supernatants (UV-B irradiated and no transmission to fibroblasts) from infected mature moDC cultures inhibit T-cell proliferation in the MLR in response to stimulation by uninfected mature moDCs (left; one experiment of 6 with similar results). The inhibitory effect of the supernatant was dose dependent (right). Each panel also includes infected moDCs as a positive control. Note that the y-axes use log₂ scales to depict T-cell proliferation based on 3HTdR incorporation (cpm) during the last 8 to 12 hours of a 5-day alloMLR culture. Error bars indicate SD.