# B-type natriuretic peptide attenuates TLR-induced cytokine and chemokine secretion in monocyte-derived Langerhans cells

## TL;DR

B-type natriuretic peptide reduces inflammation in skin immune cells, potentially offering a new way to manage inflammatory skin conditions.

## Contribution

The study reveals a novel immunomodulatory role of BNP in regulating Langerhans cell function and inflammation.

## Key findings

- BNP treatment reduces cytokine and chemokine production in TLR-activated Langerhans cells.
- BNP-treated Langerhans cells show enhanced migration toward lymph node chemokines.
- BNP limits T cell proliferation and NK cell migration induced by TLR-activated Langerhans cells.

## Abstract

B-type natriuretic peptide (BNP) is a well-known cardiac hormone and biomarker of heart failure, but emerging evidence suggests that it also possesses immunomodulatory properties, including a role in inflammatory skin conditions like atopic dermatitis (AD). Langerhans cells (LCs), specialized epidermal antigen-presenting cells, orchestrate cutaneous immunity and are targets of neuropeptides. In the present study, we investigated how BNP treatment during differentiation affects the activation, cytokine profile, and interaction of immune cells with moLCs subsequently activated via Toll-like receptors (TLRs).

MoLCs were differentiated in the presence or absence of BNP, followed by 24-hour activation with the TLR7/8 agonist CL075 and/or the TLR3 agonist polyinosinic:polycytidylic acid (poly(I:C)). Cell surface markers of moLCs were assessed using flow cytometry. ELISA was used to analyze the production of cytokines. The T cell proliferation-inducing ability of moLCs was detected through T cell coculture. Transwell migration experiments were conducted to elucidate the migratory capacity of moLCs, as well as the migration of other lymphocytes toward moLCs.

BNP treatment during the differentiation of moLCs did not alter the expression of activation markers; however, it significantly counteracted the robust increase in both pro- and anti-inflammatory cytokine production induced by TLR activation. Combined TLR activation significantly increased T cell proliferation capacity, and this effect was significantly diminished in moLCs differentiated in the presence of BNP. Functionally, BNP pre-treated moLCs exhibited significantly enhanced chemotaxis towards the lymph node chemokines, supporting the previously observed migratory phenotype. Transcriptomic analysis further supported this finding, demonstrating that BNP pre-treatment attenuated the inflammatory gene signature induced by TLR agonism. Furthermore, the supernatant from TLR-activated, BNP-treated moLCs showed a marked reduction in the ability to induce the migration of peripheral blood CD56+ Natural Killer (NK) cells.

We found that BNP primes moLCs toward a migratory phenotype and, upon subsequent TLR activation, exerts a potent inhibitory effect on their cytokine and chemokine production, thereby limiting their capacity to drive T cell proliferation and NK cell migration. This dual effect suggests that BNP may play a context-dependent role in skin immunity, potentially restraining inflammation while promoting LC transit to the draining lymph nodes.