Human Cytomegalorivus Induces Actin Cytoskeleton Abnormity in Infected Dendritic Cells with the Consequence of Depressed Immunological Functions.

Dendritic cells(DCs) are considered the most potent antigen presenting cells(APC) and accordingly play a crucial role in initiating and maintaining the adaptive immune response against viruses. The DCs actin cytoskeleton plays an active role in the immunological synapse and may explain the unique ability of DCs to activate resting T cells. Human cytomegalorivus (HCMV) is an important human pathogen that has long been known to induce or enhance immunosuppression in patients. The HCMV-associated defect in the cellular immune response has been attributed to alterations in the function of T lymphocytes and have an important influence upon stem cell transplantation outcome. However, the precise molecular mechanism by which HCMV alters the host immune response such as the effect on DCs is a longstanding enigma and remains to defined. In this study, we investigated the susceptibility of DCs at different stage to HCMV infection and the functional consequence thereof. At the immature stage of monocyte-derived DCs, viral immediately early antigen (IEA) mRNA and early antigen (EA)protein could be detected by RT-PCR and immunoflourescence microscopic analysis, respectively. The relative expression of IE mRNA in mature DCs was lower than immature DCs at 12h after infecion, 0.102±0.020 and 0.862±0.124, respectively (P<0.05). EA, primarily localized in nucleus, could be found in (62.32±14.20)% immature and (10.78±3.04)% immature DCs at 24h, repectively (P<0.01). pp65(CMV late antigen) positive cells in immature and mature DCs at 72h were (4.24±0.38)% and (0.82±0.13)%. However, after inducing maturation by LPS, these DCs showed no evidence of active infection. In infected DCs,β-actin got a significant and gradual decreasing of mRNA level. Compared with uninfected group, the expression of β-actin protein decreased to (61.8±17.4)% at 96h after infection. while the ratio of globular actin (G-actin) and fibrous actin (F-actin) increased to (201.3±42.7)% at 24h. HCMV infected immature DCs were significantly impaired in their ability to endocytose FITC-labeled dextran particles detected by flow cytometry, while uninfected DCs exhibited a high endocytic capacity(approximately 40 to 50% reduction). An impaired ability of HCMV infected DCs to mature in response to LPS could be observed. Both MHC class I and II molecules on the surface of DCs were significantly downregulated after inducing maturation by LPS compared with uninfected cells,(92.0±3.9)% versus (46.4±5.0)% for MHC I molecule and (91.8±5.3)% versus (54.3±5.7)% for MHC II molecule(both P<0.05). In contrast, the costimulatory molecules CD80,CD86 were slightly upregulated,(62.4±8.3)% versus (73.8±7.4)% for CD80 and (67.3±7.6)% versus (77.8±8.9)% for CD86. The proliferative response of T cells was drastically reduced detected by BrdU incorporation, however, this reduced capacity to stimulate alloreactive T cells could be partly restored by adding actin aggregation activator PMA(2μmol/L). In summary, we propose that the infection of immature DCs allows HCMV to evade immune recognition and T cells attack. The actin cytoskeleton abnormity in infected cells may play a pivotal role in HCMV-triggered immunosuppression.