Cellular responses to bacterial lipopolysaccharide: LPS facilitates priming of antigen-reactive T cells

Anisomycin inhibits the behaviors of T cells and the allogeneic skin transplantation in mice

There is still a lack of a high potent and low toxic immunosuppressive drug. We accidentally found that a quite low dose of anisomycin was sufficient to block proliferation of T cells. In this study, carboxy-fluorescein diacetate-succinimidyl ester staining showed that over 10.0 ng/mL of anisomycin markedly inhibited the proliferation of T cells induced by ConA. Propidium iodide staining revealed that anisomycin led to G0/G1 arrest and blocked S phase entry stimulated by ConA or phorbol 12, 13-dibutyrate plus ionomycin. Anisomycin down-regulated remarkably the CD69 and CD25 expression on the surface of T cells. The response of T cells was repressed by treatment of anisomycin, which was partly restored by adding exogenous interleukin-2, and there was no difference between anisomycin and dexamethasone, although the used dose of the latter was 100-fold of the former. The inhibition of cytotoxicity of T cells against 7919 cells by anisomycin was observed without the direct cytotoxicity to T cells or 7919 cells. The level of transforming growth factor-beta1 fell by <80.0 ng/mL in vitro and 30.0 mg/kg of anisomycin in vivo and enhanced by more than the doses. The treatment of anisomycin prolonged the survival of the transplanted skin and depressed the delayed type hypersensitivity development and the T-cell response in the skin-transplanted mice. Moreover, the effect of its restraining allograft rejection might be superior to cyclosporine A, with relatively slight toxic signs. These results indicate anisomycin significantly inhibits the behaviors of T cells and the transplantation rejection, providing important evidence for anisomycin as a novel immunosuppressant.

Cyclic ADP-ribose is a second messenger in the lipopolysaccharide-stimulated proliferation of human peripheral blood mononuclear cells

Cyclic ADP-ribose (cADPR), a universal calcium mobilizer from intracellular stores, was recently demonstrated to stimulate proliferation of various cell types. The role of cADPR in a specific process of monocyte- and plasma-mediated activation of T-lymphocytes by lipopolysaccharide (LPS) was addressed using human mononuclear cells from peripheral blood (PBMCs). Incubation of PBMCs with 0.1 microg/ml of LPS for 24 h provided a doubling in the intracellular levels of cADPR as compared with unstimulated PBMCs. The cADPR increase was abolished either by prior removal of monocytes or by pre-incubating a whole PBMC population with a monoclonal antibody against the monocyte marker CD14. The increased concentrations of intracellular cADPR elicited by LPS stimulation were paralleled by significant increases in NAD+ levels and in the activities of ectocellular and membrane-bound fractions of ADP-ribosyl cyclase/cADPR hydrolase activities. A cytosolic ADP-ribosyl cyclase was also detectable in PBMCs and its activity was comparably enhanced by LPS stimulation. This soluble cyclase is distinguished from the membrane-bound cyclase by both substrate and inhibitor sensitivities. LPS-stimulated PBMCs showed 2-3-fold increases of intracellular calcium ([Ca2+]i), and these changes were prevented completely by the cADPR antagonist 8-Br-cADPR and by ryanodine. Both compounds, and the cyclase inhibitor nicotinamide, significantly inhibited the T-lymphocyte proliferation induced by LPS in PBMCs. These results demonstrate that cADPR plays a role of second messenger in the adaptive immune recognition process of LPS-stimulated proliferation of PBMCs.