The soluble cytoplasmic tail of CD45 regulates T-cell activation via TLR4 signaling.

The soluble cytoplasmic tail of CD45 (ct-CD45) is a cleavage fragment of CD45, that is generated during the activation of human phagocytes. Upon release to the extracellular space, ct-CD45 binds to human T cells and inhibits their activation in vitro. Here, we studied the potential role of TLR4 as a receptor for ct-CD45. Treatment of Jurkat TLR4/CD14 reporter cells with ct-CD45 induced the upregulation of the reporter gene NFκB-eGFP and could be blocked by inhibitors of TLR4 signaling. Conversely, ct-CD45 did not promote the NFκB-controlled eGFP induction in reporter cells expressing TLR1, TLR2, and TLR6 transgenes and did not lead to the activation of the transcription factors NFκB, AP-1, and NFAT in a Jurkat reporter cell line expressing endogenous TLR5. Moreover, ct-CD45 binds to recombinant TLR4 in an in vitro assay and this association was reduced in the presence of oxidized 1-palmitoyl-2-arachidonyl-sn-glycero-3-phosphorylcholine. Blockade of TLR4 with mAb HTA125 partially reversed the ct-CD45-mediated inhibition of T-cell proliferation. Interestingly, targeting of TLR4 with mAb W7C11 also suppressed T-cell proliferation. In summary, the results of this study demonstrate that ct-CD45 acts via a noncanonical TLR4 activation pathway on T cells, which modulates TCR signaling.

Regulation of the Immune Cell Repertoire in Psoriasis Patients Upon Blockade of IL-17A or TNFα.

INTRODUCTION: Targeting of the proinflammatory cytokine interleukin 17A (IL-17A) or tumor necrosis factor alpha (TNFα) with the monoclonal antibodies (mAbs) ixekizumab or adalimumab, respectively, is a successful therapy for chronic plaque psoriasis. The effects of these treatments on immune cell populations in the skin are largely unknown. METHODS: In this study, we compared the composition of cutaneous, lesional and non-lesional immune cells and blood immune cells in ixekizumab- or adalimumab-treated patients with psoriasis. RESULTS: Our data reveal that both treatments efficiently downregulate T cells, macrophages and different subsets of dendritic cells (DCs) in lesional skin towards levels of healthy skin. In contrast to lesional skin, non-lesional areas in patients harbor only few or no detectable DCs compared to the skin of healthy subjects. Treatment with neither ixekizumab nor adalimumab reversed this DC imbalance in non-lesional skin of psoriatic patients. CONCLUSION: Our study shows that anti-IL-17A and anti-TNFα therapy rebalances the immune cell repertoire of lesional skin in psoriatic patients but fails to restore the disturbed immune cell repertoire in non-lesional skin.