Missing Immune Protein May Explain How H. Pylori Turns Into Cancer

If you have ever tested positive for the stomach bacterium Helicobacter pylori (H. pylori) and been told to just take an antibiotic and move on, you have probably wondered how something so common turns dangerous in the small number of people who develop stomach cancer from it. A new laboratory study offers a concrete mechanistic answer for one of the rarest of those outcomes, gastric MALT lymphoma (mucosa-associated lymphoid tissue lymphoma, a slow-growing cancer of the immune tissue in the stomach lining). Researchers found that losing a single immune protein can flip stomach-resident immune cells from cancer fighters into cancer enablers, and that the switch runs through two receptors that are already being explored as cancer drug targets elsewhere in oncology.

Key takeaways:

• Mice and human immune cells missing the protein NLRC5 develop macrophages (immune cells that normally engulf pathogens and debris) that behave like tumor allies instead of tumor fighters.
• The reprogrammed cells clear dying cells more aggressively, pump out anti-inflammatory signals, and become worse at showing the immune system's T cells what to attack.
• Blocking two receptors on these cells, AXL and MERTK, with experimental inhibitor drugs reversed much of the effect in the lab.
• This is animal and cell-line evidence only; it has not been tested in H. pylori patients, and gastric MALT lymphoma remains rare.

NLRC5 Loss Reprograms Macrophages Into Tumor-Promoting Cells

Losing a working copy of NLRC5 (an innate immune protein best known for helping cells present threats to the immune system) reprograms stomach-associated macrophages into a tumor-promoting state, according to a study published in The FASEB Journal by researchers at Monash University and the Hudson Institute of Medical Research in Australia, working with collaborators in Canada and Germany. H. pylori is classified as a bacterial carcinogen and is the leading cause of infection-related cancer worldwide, and chronic infection is implicated in over 90% of cases of gastric MALT lymphoma, the most common type of lymphoma that arises outside the lymph nodes. The research team showed that macrophages lacking NLRC5 take on the hallmarks of tumor-associated macrophages (TAMs), a category of immune cells known in cancer biology for helping tumors evade the immune system rather than fight it.

Why This Matters for Anyone Managing a Chronic H. Pylori Infection

Most people carrying H. pylori will never develop lymphoma, since gastric MALT lymphoma has an incidence of fewer than 15 cases per 100,000 people per year, according to the study authors. But for the minority in whom chronic infection progresses toward this cancer, this research offers one of the first mechanistic explanations for why the immune system fails to clear the threat in time. If confirmed in later work, it suggests that some individuals' risk may hinge less on the bacteria itself and more on how their own macrophages are wired to respond to it, since NLRC5 activity determines whether those cells stay in a cancer-fighting mode or drift toward a cancer-tolerating one.

How Researchers Modeled Stomach Lymphoma in Mice and Human Cells

The team used mice engineered to lack NLRC5 specifically in myeloid immune cells (called Nlrc5 mø-KO mice), a model that develops MALT-like lesions within 3 months of infection, compared with 12 to 24 months in standard mouse models of the disease. Mice were infected with Helicobacter felis, a mouse-adapted relative of H. pylori, using about 10 million bacteria (10⁷ colony-forming units) delivered orally, then examined 12 weeks later. To confirm the findings translate beyond mice, the team also used human THP-1 macrophages edited with CRISPR gene-editing technology to remove NLRC5, then exposed them to H. pylori and H. felis in dish-based coculture experiments. Both the mouse spleen-derived macrophages and the human macrophages showed the same pattern: significantly higher expression of the receptor proteins AXL and MERTK, the two TAM marker receptors most associated with immune suppression, while a third related receptor, TYRO3, was unaffected.

What the Finding Means and Does Not Mean for Your Own Gut Health

For a reader currently managing an H. pylori diagnosis, IBS, or another gut-related concern, the practical takeaway is narrow but still useful: this study does not change current treatment guidance. Chronic H. pylori infection is still best addressed by eradicating the infection with antibiotics, which remains the established first-line approach for early-stage MALT lymphoma when the bacteria are present. Nothing in this study identifies a supplement, diet, or over-the-counter intervention that restores NLRC5 function or blocks AXL and MERTK, so there is no self-directed action to take based on these findings today. What is worth discussing with a doctor is simply standard practice already, persistent stomach symptoms, a positive H. pylori test, or a family history of gastric lymphoma warrant an in-person workup rather than a wait-and-see approach.

The Big Caveats: This Is Animal and Cell-Line Evidence So Far

The authors are explicit that their model has real limits. The H. pylori and H. felis strains used lack a functional type IV secretion system, a bacterial structure important for virulence in naturally occurring human infections, so the mouse model may not capture the full aggressiveness of real-world strains. The effect was also cell-type specific: bone marrow-derived macrophages grown in the lab from the same NLRC5-deficient mice did not show the enhanced efferocytosis (the technical term for a cell engulfing and clearing dying cells) seen in spleen-derived macrophages, meaning the tissue environment a macrophage develops in matters. Because gastric MALT lymphoma is rare, with national surveillance data showing it has been declining in the US over the past two decades, the authors note that obtaining matched patient tissue samples to directly confirm the mechanism in humans is difficult, and they call for future work restoring NLRC5 in these cells to see if it reverses the tumor-permissive phenotype.

TAM-Targeting Drugs Could Be a Future Research Direction

The strongest experimental support for the mechanism came from reversing it. When researchers treated NLRC5-deficient human macrophages with small-molecule inhibitors of AXL (R428) and MERTK (UNC2025), the cells' engulfment of dying cells dropped back down, along with signaling through the downstream proteins STAT3 and ERK1/2. AXL and MERTK are already under investigation as drug targets in several other cancer types because of their role on tumor-associated macrophages, which the authors suggest could eventually open a therapeutic angle specific to H. pylori-driven lymphoma, though no such drug has been tested in that context yet. The study was funded entirely by public research bodies, including the US Department of Defense and Australia's National Health and Medical Research Council, and the authors reported no conflicts of interest.

Common Questions

Does everyone with H. pylori eventually develop this lymphoma? No. The large majority of people with H. pylori never develop MALT lymphoma; the cancer affects fewer than 15 people per 100,000 each year even though the bacterium itself is extremely common.

What exactly does NLRC5 normally do? NLRC5 is an innate immune protein that helps cells display internal threats to the immune system's surveillance machinery, a process called antigen presentation, and this study shows it also keeps macrophages from drifting into a tumor-tolerant state.

Could this lead to a new treatment? Not yet. The AXL and MERTK inhibitors used here are lab research tools, not approved drugs for this condition, though the pathway they target is already being pursued in other cancers.

Does this apply to people without H. pylori? The mechanism described here was specifically triggered by Helicobacter infection in this model, so it does not establish a role for NLRC5 loss in cancers unrelated to H. pylori or Helicobacter species.

References

1. Shambel Araya Haile, Alessandra Gatta, Nina Colon, et al. (2026). NLRC5 ‐Deficient Macrophages Promote a Tumor‐Permissive Phenotype via AXL ‐ and MERTK ‐Mediated Efferocytosis. The FASEB Journal. https://doi.org/10.1096/fj.202504879r
2. Ju Seok Kim, Sun Hyung Kang, Hee Seok Moon, Jae Kyu Sung, Hyun Yong Jeong (2016). Clinical Outcome of Eradication Therapy for Gastric Mucosa-Associated Lymphoid Tissue Lymphoma according toH. pyloriInfection Status. Gastroenterology Research and Practice. https://doi.org/10.1155/2016/6794848
3. Yafang Lai, Haoting Shi, Zixin Wang, et al. (2022). Incidence trends and disparities in Helicobacter pylori related malignancy among US adults, 2000–2019. Frontiers in Public Health. https://doi.org/10.3389/fpubh.2022.1056157
4. Kayla V. Myers, Sarah R. Amend, Kenneth J. Pienta (2019). Targeting Tyro3, Axl and MerTK (TAM receptors): implications for macrophages in the tumor microenvironment. Molecular Cancer. https://doi.org/10.1186/s12943-019-1022-2