NFAT Reporter THP-1 Cells

Cell line description

THP1-Lucia™ cells were derived from the human THP-1 monocyte cell line by stable integration of an NFAT-inducible Lucia® reporter construct. THP1-Lucia™ NFAT cells feature the Lucia luciferase gene, a secreted luciferase reporter gene, under the control of an ISG54 minimal promoter fused to six NFAT response elements. 

As a result, THP1-Lucia™ NFAT cells allow the monitoring of NFAT activation by determining the activity of Lucia® luciferase. The levels of NFAT-induced Lucia® in the cell culture supernatant are readily assessed with QUANTI-Luc™ 4 Lucia/Gaussia, a Lucia® and Gaussia luciferase detection reagent. As THP-1 cells represent innate immune monocytes, they express a variety of pattern recognition receptors (PRRs). Thus, THP1-Lucia™ NFAT cells induce the activation of NFAT in response to PRR-ligands as well as cell-permeable small molecules (e.g., Ionomycin).

NFAT in Myeloid Cells

The nuclear factor of activated T cells (NFAT) comprises a family of transcription factors originally described as regulators of interleukin-2 (IL-2) expression in T cells [1]. In resting cells, NFATs are maintained in an inactive state in the cytosol. NFAT activation in innate immune cells, such as dendritic cells (DCs) and macrophages, can occur following ligation of several pattern recognition receptors (PRRs), including the TLR4–CD14 complex, TLR9, NOD-1, and dectin‐1 [2-3]. Subsequent increased intracellular calcium flux activates calmodulin, which in turn stimulates the phosphatase calcineurin. Activated calcineurin dephosphorylates NFAT, allowing its nuclear translocation, where it cooperates with transcription factors such as AP-1 to drive gene expression [4]. In innate immune cells, the key functions of NFAT are linked to phagocytosis, cytokine production (e.g. IL-2, IL-10, TNF-α), and antifungal defense [2]. 

Implications for Immunosuppression

Calcineurin/NFAT inhibitors, such as cyclosporine A (CsA) and tacrolimus (FK506), are primarily used to prevent allograft rejection and to treat GVHD after bone marrow transplantation. These drugs are also used to treat a wide variety of immune disorders that include atopic dermatitis and refractory colitis [2]. The immunosuppressive state induced by these drugs is mainly achieved by inhibition of T cell cytokine production and limits the release of IL-2 [2]. 

Despite their clinical value, the broad inhibition of NFAT signaling comes at a cost. Patients receiving calcineurin inhibitors show markedly increased susceptibility to bacterial and fungal infections [4]. Indeed, severe invasive fungal infections occur in ∼3% of post‐transplant patients per year, leading to death in almost 40% of affected patients [3]. This increase in susceptibility towards microbial infections has been considered for a long time to be largely non-specific [4]. However, accumulating evidence suggests that they are not solely a consequence of impaired T cell responses but also reflect compromised myeloid cell function [1-4].

Further research into NFAT signaling in myeloid cells will not only refine our understanding of innate immunity but also pave the way for safer, more tailored immunosuppressive regimens.

1. Fric J, et al., 2012. Calcineurin/NFAT signalling inhibits myeloid haematopoiesis. EMBO Mol Med. (4):269-82.
2. Fric J, et al., 2012. NFAT control of innate immunity. Blood. 120(7):1380-9. 
3. Bendíčková K, et al., 2020. Calcineurin inhibitors reduce NFAT-dependent expression of antifungal pentraxin-3 by human monocytes. J Leukoc Biol. 107(3):497-508. 
4. Vandewalle A, et al., 2014. Calcineurin/NFAT signaling and innate host defence: a role for NOD1-mediated phagocytic functions. Cell Commun Signal. 12:8.