You (bacteria) shall not pass: NLRP6 can sense you! - News & Views - NLRP6 detection role in bacterial spread

Sep 28, 2026

Intracellular bacteria can spread directly from one host cell to the next, bypassing extracellular immune defenses and thereby worsening infection outcomes. In this News & Views, Boegli and colleagues reveal that the innate immune sensor NLRP6 detects bacteria-induced lysosomal damage and triggers cytokine release or cell death. The article explains how cell-to-cell transmission evades extracellular mediators, then describes NLRP6’s inflammasome assembly, caspase-1 activation, and pyroptotic gasdermin cleavage to both warn the host and disrupt bacterial hiding.

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CategoryHealthcare

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News & Views

NLRP6 senses lysosomal damage and triggers immune responses

Cell-to-cell spread and intracellular danger sensing by NLRs

Past debates and multifaceted NLRP6 sensing capabilities

News & Views You (bacteria) shall not pass: NLRP6 can sense you! Alexander N R Weber 1,2,3,4 ✉ & Philip Rosenstiel 5 ✉ The ability of intracellular bacteria to spread directly from one cell to the next, avoiding extracellular immune defensesand drugs, is essential for pathogen dissemination and, ultimately, the progression and severity of infection. In this issue of The EMBO Journal, Boegli and colleagues uncover a previously unrecognized role of the enigmatic innate immune sensor NLRP6 in detecting bacteria-induced lysosomal damage and triggering cytokine release or cell death to limit infection. See also: A Boegli et al Bacteria attempting to spread within a multicellular host face multiple chal lenges as they seek out protected niches that shield them from direct immune defense mechanisms. Extracellularly, they may be especially vulnerable to a whole arsenal of immune mediators, e.g., antimicrobial peptides, complement proteins, antibodies, or phagocytes. For invasive pathogens, including species of Listeria, Shigella, Orientia, Chlamydia, and Salmonella, a far safer route for spreading while avoiding the risks of the extracellular space, is direct cell-to-cell transmission from an infected host cell to its neighbor. For example, Listeria and Shigella propel themselves from the plasma membrane of an infected cell into the plasma membrane of an adjacent cell using the force generated by actin-based motility, and then become engulfed into a vacuole before escaping into the cytosol of the neighboring cell. However, the host has evolved an additional layer of defense involving a distinct family of cytosolic pattern-recognition receptors (PRRs) known as Nod-like receptors (NLRs) . These intracellular sentinels can recognize speciﬁc microbe- or pathogenassociated molecular patterns (MAMPs or PAMPs, respectively), such as bacterial cellwall components (e.g., muramyl dipeptide or ﬂagellin), once these signals cross the membrane barrier and enter the cytosol. An alternative strategy of danger sensing by NLRs is the detection of cellular stress signals that reﬂect perturbations in homeostasis, e.g., potassium efﬂux, ROS, or ATP levels. Although the family member NLRP6 had also been proposed to sense infections through recognition of speciﬁc MAMPs, Boegli et al now suggest that NLRP6 sensesan infection-relevant process rather than a microbe-speciﬁc molecule (Fig. 1) . Speciﬁ cally, they show that NLRP6 can function asan intracellular “trip-wire” for incoming bacteria seeking to enter via a neighboring cell. It does so by assembling a so-called inﬂammasome, a multiprotein complex that bridges the sensor, NLRP6, to an enzyme, caspase-1, that is able to mature inﬂammatory cytokines (e.g., IL-1β or IL-18) for subsequent release, and to cleave gasdermin (GSDM) family proteins to execute pyroptotic, i.e., inﬂammatory, cell death. The effect is twofold: raising an alarm to infection and shutting down the bacterial hiding place. The description of NLRP6 as a sensor for cell-to-cell spread was unexpected. NLRP6 (initially named PYPAF5) was ﬁrst proposed not to act as a bona ﬁde PRR but rather as a transcriptional regulator of other PRRs (Grenier et al, 2002) and a negative regulator of inﬂammatory signaling during bacterial pathogen clearance, including Listeria spp. (Anand et al, 2012) . Only subsequently, NLRP6 was suggested to directly respond to certain metabolites (e.g., taurine, Levy et al, 2015) or a MAMP, namely double-stranded RNA from intestinal viruses (Wang et al, 2015), in intestinal epithelial cells (IECs), where it is most prominently expressed in both humans and mice. However, direct ligand binding and the underlying molecular mechanisms remained unclear until more recently, when RNA was shown to bind NLRP6 in vitro and trigger phase-separation as a potential way of bringing together a sufﬁcient number of NLRP6 molecules to form an inﬂammasome (Shen et al, 2021) . Apart from IECs (Levy et al, 2015), a role

FAQs

Why is cell-to-cell spread by intracellular bacteria important for infection progression?

It allows bacteria to move directly between host cells while avoiding extracellular immune defenses and drug exposure. This helps sustain dissemination and increases infection severity.

What new role of NLRP6 is highlighted in this issue?

NLRP6 is described as sensing bacteria-induced lysosomal damage and then triggering cytokine release or cell death to limit infection.

How does NLRP6 drive the immune outcome once it detects the relevant signal?

NLRP6 assembles an inflammasome that links the sensor to caspase-1, enabling maturation and release of inflammatory cytokines and cleavage of gasdermin proteins to execute pyroptotic cell death.

Sep 28, 2026

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