Interferon-gamma downregulates the proliferative response of hapten-specific B cells stimulated by antigen and cytokines

Ultraviolet B but Not A Radiation Activates Suppressor B Cells in Draining Lymph Nodes

Immunosuppressive doses of solar-simulated UV radiation activate lymph node B cells that can suppress primary immunity by inhibiting the function of dendritic cells. The aim of this study was to determine the waveband responsible for activation of these suppressor B cells. We exposed C57BL/6 mice to various doses of either UVA or UVB radiation and analyzed the number and activation state of lymph node antigen-presenting cells (APC). Immunosuppressive doses of UVB but not UVA activated B cells as assessed by major histocompatibility complex II (MHC II) expression and doubled their numbers in draining lymph nodes. Higher doses of UVA that were not immunosuppressive actually suppressed B cell activation. Our results show that UVA and UVB suppress systemic immunity via different mechanisms. Lymph node B cells are activated in response to immunosuppressive doses of UVB but not UVA. Thus, the activation state of lymph node APC appears to be important for UV immunomodulation.

IFN-γ Down-Regulates MHC Expression and Antigen Processing in a Human B Cell Line

IFN-γ is a crucial mediator in the induction of cell-mediated Th1-type responses but is predominantly a negative regulator of B cell differentiation and proliferation. This cytokine is therefore a key factor in determining Th1 vs Th2 differentiation. This study investigates the action of IFN-γ in modulation of HLA-DR expression and Ag presentation by EBV-transformed human B cell lines. In contrast to its action on the monocyte/macrophage, IFN-γ down-regulates surface MHC expression on these B cells, and this regulation is posttranscriptional. In parallel with MHC down-regulation, there is a reduced capability to process and present exogenous protein and peptide Ag to T cell hybridomas. IFN-γ does not change the rates of fluid phase endocytosis or exocytosis in this model system but correlates with an up-regulation of the lysosomal enzymes cathepsins B and D.