Expansion of antigen-specific regulatory T cells with the topical vitamin d analog calcipotriol.

1,25-Dihydroxyvitamin D(3) is immunosuppressive both in vivo and in vitro. Topical vitamin D analogs such as calcipotriol alter keratinocyte function, but their effects on cutaneous immune responses are less well understood. We demonstrate that exposure of the skin to calcipotriol before transcutaneous immunization with OVA protein and CpG adjuvant prevents Ag-specific CD8(+) T cell priming coincident with Langerhans cell depletion in the skin. Immunization through calcipotriol-treated skin induces CD4(+)CD25(+) regulatory T cells (Treg) that prevent subsequent Ag-specific CD8(+) T cell proliferation and IFN-gamma production. Treg induced by calcipotriol are able to inhibit the induction and the elicitation of protein contact hypersensitivity. Topical calcipotriol treatment also induces RANKL (receptor activator of NF-kappaB ligand) expression by keratinocytes, a TNF family member involved in modulation of skin dendritic cells. UV light B induces Ag-specific tolerance when it is applied before transcutaneous immunization. We suggest that UV light B-induced tolerance is induced via a vitamin D receptor-dependent mechanism as vitamin D receptor (VDR) knockout mice fail to increase FoxP3(+) Treg in their peripheral draining lymph node following irradiation. Additionally, keratinocytes of VDR(-/-) mice fail to induce RANKL upon UV irradiation or calcipotriol treatment. The in vivo expansion of Ag-specific Treg with the topical application of the vitamin D analog calcipotriol followed by transcutaneous immunization is a simple method to augment functional Ag-specific CD4(+)CD25(+)Foxp3(+) Treg populations and mimics Ag-specific UV-induced tolerance.

Molecular clamp mechanism of substrate binding by hydrophobic coiled-coil residues of the archaeal chaperone prefoldin.

Prefoldin (PFD) is a jellyfish-shaped molecular chaperone that has been proposed to play a general role in de novo protein folding in archaea and is known to assist the biogenesis of actins, tubulins, and potentially other proteins in eukaryotes. Using point mutants, chimeras, and intradomain swap variants, we show that the six coiled-coil tentacles of archaeal PFD act in concert to bind and stabilize nonnative proteins near the opening of the cavity they form. Importantly, the interaction between chaperone and substrate depends on the mostly buried interhelical hydrophobic residues of the coiled coils. We also show by electron microscopy that the tentacles can undergo an en bloc movement to accommodate an unfolded substrate. Our data reveal how archael PFD uses its unique architecture and intrinsic coiled-coil properties to interact with nonnative polypeptides.