Reduced CD18 Levels Drive Regulatory T Cell Conversion into Th17 Cells in the CD18hypo PL/J Mouse Model of Psoriasis

Abstract

Defective development and function of CD4+CD25high+Foxp3+ regulatory T cells (Tregs) contribute to the pathogenesis of psoriasis and other autoimmune diseases. Little is known about the influence of adhesions molecules on the differentiation of Foxp3+ Tregs into proinflammatory Th17 cells occurring in lesional skin and blood of psoriasis patients. In the CD18hypo PL/J mouse model of psoriasis, reduced expression of CD18/β2 integrin to 2–16% of wild-type levels is associated with progressive loss of Tregs, impaired cell–cell contact between Tregs and dendritic cells (DCs), as well as Treg dysfunction as reported earlier. In the present investigation, Tregs derived from CD18hypo PL/J mice were analyzed for their propensity to differentiate into IL-17–producing Th17 cells in vivo and in in vitro Treg–DC cocultures. Adoptively transferred CD18hypo PL/J Tregs were more inclined toward conversion into IL-17–producing Th17 cells in vivo in an inflammatory as well as noninflammatory environment compared with CD18wt PL/J Tregs. Addition of neutralizing Ab against CD18 to Treg–DC cocultures in vitro promoted conversion of CD18wt PL/J Tregs to Th17 cells in a dose-dependent manner similar to conversion rates of CD18hypo PL/J Tregs. Reduced thymic output of naturally occurring Tregs and peripheral conversion of Tregs into Th17 cells therefore both contribute to the loss of Tregs and the psoriasiform dermatitis observed in CD18hypo PL/J mice. Our data overall indicate that CD18 expression levels impact Treg development as well as Treg plasticity and that differentiation of Tregs into IL-17–producing Th17 cells is distinctly facilitated by a subtotal deficiency of CD18.

Reduction of CD18 Promotes Expansion of Inflammatory γδ T Cells Collaborating with CD4+ T Cells in Chronic Murine Psoriasiform Dermatitis

“…A critical role of CD4 + T cells in psoriasiform dermatitis of CD18 hypo PL/J mice was previously confirmed by resolution of skin disease after treatment anti-CD4 Abs (31). Moreover, enhanced regulatory T cell (Treg)/Th17 conversion in lesional skin and secondary lymphoid organs on the CD18 hypo PL/J background could be detected (40), and adoptive transfer of CD18 wt Tregs, but not CD18 hypo Tregs, significantly ameliorated CD18 hypo PL/J psoriasiform dermatitis (32). In the present investigation, we used this spontaneous and chronic psoriasis mouse model to dissect the roles of CD4 + and gd T cells and to investigate potential interactions between both T cell subsets and showed a new critical role for wild-type CD18 levels in suppression of inflammatory gd T cells.…”

“…Importantly, we could previously demonstrate that numbers of natural Tregs progressively decline in CD18 hypo PL/J mice and that suppressive activity of Tregs is diminished as a consequence of impaired TGF-b production (32). More recently, enhanced conversion of CD18 hypo PL/J Tregs into Th17 in psoriasiform skin and lymph nodes has been identified as additional pathomechanism (40). From these data, we conclude that suboptimal CD18 levels on T cells might generally increase plasticity and favor inflammatory properties via expression of RORgt and IL-17 secretion while suppressing regulatory properties mediated by Foxp3 and TGF-b and thereby contribute to manifestation of autoimmune diseases (69,70).…”

“…Isotype IgG was used as control for all experiments. Cells isolated from thymi, spleens, or lymph nodes of CD18 wt PL/J and CD18 hypo PL/J mice were processed for FACS analysis as previously described und subjected to intracellular staining (ICS) for detection of IL-17 or Foxp3 as indicated (32,40). All FACS analyses were performed using an FACSCanto System (BD Biosciences) and FACSDiva Software as well as FlowJo software (Tree Star).…”

“…Isolation of total cellular RNA from skin or lymph nodes (TriFast solution; Peqlab), cDNA generation (SuperScript Vilo cDNA Synthesis Kit; Invitrogen) and quantitative real-time RT-PCR (qPCR; LightCycler FastStart DNA Master PLUS SYBR Green I Supermix; Roche) were performed according to the manufacturers' instructions as previously described (40). Samples were analyzed in triplicate by qPCR with a LightCycler (Roche) using cytokine or marker gene specific primers for 40 amplification cycles, and gene expression levels were calculated by normalization of data to GAPDH mRNA expression.…”

“…Immunofluorescence staining of murine skin and lymph node samples Fixation, staining, and microscopy of frozen cryosections (5 mm) of mouse back skin were performed as previously described (40). To detect T cell subpopulations, sections were first incubated with Ab against mouse CD4 (clone-L3T4; eBioscience) or mouse gdTCR (BD Pharmingen) and appropriate secondary Abs.…”