Calcineurin-NFAT signalling in myeloid leucocytes: new prospects and pitfalls in immunosuppressive therapy

Calcineurin-NFAT signalling in myeloid leucocytes: new prospects and pitfalls in immunosuppressive therapy

Myeloid leucocytes mediate host protection against infection and critically regulate inflammatory responses in body tissues. Pattern recognition receptor signalling is crucial for myeloid cell responses to pathogens, but growing evidence suggests an equally potent role for Calcineurin–NFAT signalling in control of myeloid cell function. All major subsets of myeloid leucocytes employ Calcineurin–NFAT signalling during immune responses to pathogens and/or tissue damage, but the influence this pathway exerts on pathogen clearance and host susceptibility to infection is not fully understood. Recent data from experimental models indicate that Calcineurin‐NFAT signalling is essential for infection control, and calcineurin inhibitors used in transplantation medicine (including cyclosporine A and tacrolimus) are now being tested for efficacy in a diverse range of inflammatory conditions and autoimmune pathologies. Efforts to repurpose calcineurin inhibitor drugs for new therapeutic applications may yield rapid improvements in clinical outcomes, but the potential impact of these compounds on myeloid cell function in treated patients is largely unknown. Here we discuss Calcineurin–NFAT control of myeloid leucocyte function in the context of recent therapeutic developments and ongoing clinical studies.

Expression of PBMC TLR4 in Renal Graft Recipients Who Experienced Delayed Graft Function Reflects Dynamic Balance Between Blood and Tissue Compartments and Helps Select a Problematic Patient

Both Toll-like receptor 4 (TLR4) and monocytes focus stimuli, causing them to contribute differently to chronic injury of a transplanted kidney.

AIM

The aim of our study was to determine if TLR4 monocyte is a diagnostic tool and possibly a target for therapeutic intervention.

MATERIALS

We studied 143 kidney transplant (KT) patients (88 male, 55 female; 50.3 ± 12.8 years); median was 10.4 post KT, follow-up was 11.4 months, and 46 patients had delayed graft function (DGF+) history. Control group (38 healthy volunteers) had monocyte mRNA-TLR4 expression (TLR4ex). DGF+ were divided by median of TLR4ex (-0.1034) into 2 groups: low-TLR4 expression (L-TLR4ex) and high-TLR4 expression (H-TLR4ex).

RESULTS

We showed that in comparison with DGF-, the DGF+ had much lower TLR4ex, and worse KT function both currently (TLR-day) (serum creatinine [sCr] P = .002; estimated glomerular filtration rate [eGFR] P = .001) and post follow-up (sCr P = .006; eGFR P = .005). The DGF+ with L/H-TLR4ex comparison showed no differences in TLR-day KT function but did show differences in post follow-up (sCr P = .01; eGFR P = .02; ΔeGFR% P = .001). Regression analysis showed an association between recipient age, tacrolimus concentration, and uremic milieu (ie, TLR-day sCr and GFR with TLR4ex). Reverse regression analysis indicated an association of TLR4ex (especially L/H-TLR4ex) with post follow-up parameters of KT function and numeric/qualitative measures of change.

CONCLUSION

DGF affects the fate of a graft. Within a several months after transplantation, TLR4ex of peripheral blood mononuclear cells declines in DGF patients. Low LR4ex in patients with DGF+ is associated with poor prognosis for the efficiency of the KT. In patients with DGF+, the proper selection of immunosuppression (tacrolimus dosing) is very important. Higher concentrations of tacrolimus may improve prognosis. The analysis of TLR4ex change may be a useful parameter for the real assessment of immunosuppression efficacy. It is important for transplanted organ function that peripheral blood mononuclear cells effectively leave circulation and remain in the graft.

Calcineurin B in CD4+ T Cells Prevents Autoimmune Colitis by Negatively Regulating the JAK/STAT Pathway

Calcineurin (Cn) is a protein phosphatase that regulates the activation of the nuclear factor of activated T-cells (NFAT) family of transcription factors, which are key regulators of T-cell development and function. Here, we generated a conditional Cnb1 mouse model in which Cnb1 was specifically deleted in CD4⁺ T cells (Cnb1^CD4 mice) to delineate the role of the Cn–NFAT pathway in immune homeostasis of the intestine. The Cnb1^CD4 mice developed severe, spontaneous colitis characterized at the molecular level by an increased T helper-1-cell response but an unaltered regulatory T-cell compartment. Antibiotic treatment ameliorated the intestinal inflammation observed in Cnb1^CD4 mice, suggesting that the microbiota contributes to the onset of colitis. CD4⁺ T cells isolated from Cnb1^CD4 mice produced high levels of IFNγ due to increased activation of the JAK2/STAT4 pathway induced by IL-12. Our data highlight that Cn signaling in CD4⁺ T cells is critical for intestinal immune homeostasis in part by inhibiting IL-12 responsiveness of CD4⁺ T cells.