Heat shock protein 70 potentiates interferon alpha production by plasmacytoid dendritic cells: relevance for cutaneous lupus and vitiligo pathogenesis

BACKGROUND

Plasmacytoid dendritic cells (pDCs) are a subset of dendritic cells specialized in the production of type I interferon (IFN-α/β) and involved in various cutaneous inflammatory and autoimmune disorders, such as cutaneous lupus erythematosus (CLE) and vitiligo. Heat shock proteins (HSPs) are molecular chaperones essential for maintaining cellular functions, but they can act as a danger signal during inflammation.

OBJECTIVES

To decipher the role of HSP70 in the production of IFN-α by pDCs in CLE and vitiligo.

METHODS

Expression of HSP70 and CD123⁺ pDCs was analysed by immunohistochemistry or immunofluorescence in CLE and vitiligo skin samples. Flow cytometry was performed to analyse expression of HSP70 receptors, activation markers on pDCs and DNA uptake by pDCs in the presence of HSP70. The impact of HSP70 on DNA-induced IFN-α secretion by pDCs was evaluated by enzyme-linked immunosorbent assay (ELISA). The effect of IFN-α on chemokine (C-X-C motif) ligand 9 (CXCL9)/10 gene and protein expression by keratinocytes was determined by real-time polymerase chain reaction and ELISA.

RESULTS

Infiltration of pDCs in CLE and progressive vitiligo was primarily located in the epidermis, close to keratinocytes expressing HSP70. In vitro experiments revealed that the pDCs expressing HSP70 receptor Lox-1 (lectin-like oxidized low-density lipoprotein-receptor-1) were able to aggregate HSP70. Exogenous HSP70 induced activation of pDCs and increased the uptake of exogenous DNA. Furthermore, HSP70 potentiated DNA-induced IFN-α production by pDCs. Finally, IFN-α induced expression of CXCL9 and CXCL10 by keratinocytes.

CONCLUSIONS

These data demonstrate that interaction between HSP70 and pDCs in CLE and vitiligo is a prerequisite for the enhancement of IFN-α production, and could be an interesting target.

Nitric oxide induces the apoptosis of human BCR-ABL-positive myeloid leukemia cells: evidence for the chelation of intracellular iron

Anti-leukemia activity of human macrophages involves the generation of nitric oxide (NO) derivatives. However, leukemic transformation may involve mechanisms that rescue cells from NO-mediated apoptosis. In the present work, we analyzed the effects of exogenous NO on the proliferation of BCR-ABL(+) chronic myelogenous leukemia (CML) cells. As normal leukocytes, the proliferation of leukemia cells was inhibited by SNAP (S-nitroso-N-acetyl-penicillamine), GEA (Oxatriazolium amino-chloride), and SIN-1 (Morpholino-sydnonimine), whereas SNP (sodium nitroprusside) had no effect on leukemia cell growth. SIN-1 induced higher anti-proliferation activity in BCR-ABL(+) cells, compared to normal hemopoietic cells. Inhibition of leukemia cell proliferation correlated with increased apoptosis and DEVDase activity. The simultaneous addition of exogenous iron reversed NO-mediated inhibition of cell growth, caspase activation and apoptosis in all BCR-ABL(+) cells tested. The quantification of intracellular iron levels in leukemia cells indicated that NO induced an early, dose-dependent decrease in ferric iron levels. Accordingly, elevation of intracellular iron protected leukemia cells from NO-mediated apoptosis. Together, the present work reveals the presence of an iron-dependant mechanism for leukemia cell rescue from NO-induced growth inhibition and apoptosis.