No abstract

Dendritic cells (DCs) are recognized as major players in the regulation of immune responses to a variety of Ags, including bacterial agents. LPS, a Gram-negative bacterial cell wall component, has been shown to fully activate DCs both in vitro and in vivo. LPS-induced DC maturation involves activation of p38, extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinases, and NF-κB. Blocking p38 inhibits LPS-induced maturation of DCs. In this study we investigated the role of LPS in the in vitro generation of immature DCs. We report here that in contrast to the observed beneficial effects on DCs, the presence of LPS in monocyte culture retarded the generation of immature DCs. LPS not only impaired the morphology and reduced the yields of the cultured cells, but also inhibited the up-regulation of surface expression of CD1a, costimulatory and adhesion molecules. Furthermore, LPS up-regulated the secretion of IL-1β, IL-6, IL-8, IL-10, and TNF-α; reduced Ag presentation capacity; and inhibited phosphorylation of ERK, but activated p38, leading to a reduced NF-κB activity in treated cells. Neutralizing Ab against IL-10, but not other cytokines, partially blocked the effects of LPS. Inhibiting p38 (by inhibitor SB203580) restored the morphology, phenotype, and Ag presentation capacity of LPS-treated cells. SB203580 also inhibited LPS-induced production of IL-1β, IL-10, and TNF-α; enhanced IL-12 production; and recovered the activity of ERK and NF-κB. Thus, our study reveals that LPS has dual effects on DCs that are biologically important: activating existing DCs to initiate an immune response, and inhibiting the generation of new DCs to limit such a response.

Two common features in human immunodeficiency virus infection and acquired immunodeficiency syndrome, rheumatoid arthritis, and hematologic malignancies including multiple myeloma are elevated serum levels of ␤ 2 -microglobulin (␤ 2 M) and activation or inhibition of the immune system. We hypothesized that ␤ 2 M at high concentrations may have a negative impact on the immune system. In this study, we examined the effects of

Purpose: To develop effective immunotherapies for patients with multiple myeloma, it is important to use novel tumor antigens. Recent studies in solid tumors show that tumor-derived heat shock proteins

Multiple myeloma (MM) is a B-cell malignancy often associated with a suppressed immune system. The mechanisms for the immunosuppression are largely unknown. In this study, we examined, using the murine 5T33 myeloma model, the effects of tumor cell or its-derived factors on the differentiation and function of bone marrow-derived dendritic cells (BMDCs). Our results showed that differentiation of BMDCs was retarded in the presence of 10% of tumor-derived supernatant (TSN). This is evident by, compared with control cells, the downregulated expression of surface molecules including CD40, CD86 and MHC class II; secretion of higher levels of IL-10 and lower levels of IL-12; and a poor T-cell response in an allogeneic mixed lymphocyte reaction induced by TSN-treated cells. The same phenomenon was also observed when the bone marrow progenitor cells were cocultured, either in direct contact or separated by transwell membrane, with myeloma cells. The treatment downregulated the expression of phosphorylated extracellular signal-related kinase (ERK) and mitogen-induced extracellular kinase (MEK), and upregulated the expression of phosphorylated p38 mitogen-activated protein kinase (p38 MAPK) and signal transducer and activator of transcription-3 (STAT3) in the cells. As a high level of interleukin (IL)-10, IL-6, vascular endothelial growth factor (VEGF) and transforming growth factor (TGF)-b can be detected in TSN, we examined whether these cytokines were responsible. Our results showed that addition of TGF-b, IL-10 and/or IL-6 could largely replace TSN in retarding the differentiation of BMDCs, and neutralizing antibodies against these cytokines, especially in combination, were able to block the effects of TSN or tumor cells on BMDCs. Finally, our results showed that inhibiting p38 MAPK or STAT3 restored the differentiation and function of these cells. Hence, our study not only sheds light on the mechanisms of tumor-induced immune evasion in MM and but also provides one of the solutions to overcome the problems.