Rothia nasimurium: a bacterium that trains porcine alveolar macrophages to defend more effectively
When a pathogen enters the lungs, one of the first cell types to detect it and start acting are alveolar macrophages. These immune sentinels reside in the alveoli —the tiny sacs where gas exchange takes place— and are essential for initiating a rapid and effective antimicrobial response. But what if we could train them to be better prepared even before the pathogen arrives?
That’s the question explored by a recent study led by IRTA-CReSA: the use of immune-stimulating components to enhance the porcine immune system. Specifically, researchers are investigating the use of an inactivated commensal bacterium commonly found in the pig’s nasal microbiota, Rothia nasimurium. The goal is to determine whether treating alveolar macrophages with this bacterium can activate and “train” them to stay alert and better equipped to fight off both viral and bacterial infections. The findings point toward a new way to boost immunity naturally and preventively, improving animal health status.
A harmless bacterium that sends a powerful signal
Rothia nasimurium is a natural member of the nasal microbiota in healthy pigs. It is a commensal bacterium, meaning it coexists with the host without causing harm. Previous studies by the same research group had already suggested that this strain could stimulate immune cells.
In this new study, an inactivated form of the bacterium (incapable of replication or causing infection) was used to treat porcine alveolar macrophages. The result? The treated cells showed decreased viral replication and an enhanced innate response against two of the most important pathogens in swine health: porcine reproductive and respiratory syndrome virus (PRRSV) and African swine fever virus (ASFV).
“Trained immunity” in the innate immune system
One of the most interesting findings is that this antiviral state did not vanish immediately. Even six days after treatment with R. nasimurium, macrophages continued to respond more effectively to ASFV infection. This suggests the induction of trained immunity —a concept in which the innate immune system retains a kind of memory that enables it to react more strongly to future threats.
Unlike adaptive immune memory (involving antibodies and T cells), trained immunity involves epigenetic and metabolic reprogramming of innate immune cells, making them more responsive to subsequent infections.
Strengthening lung immunity without antibiotics
This research offers an innovative approach to improving respiratory immunity in pigs. Instead of relying solely on pathogen-specific vaccines or antibiotics, the strategy focuses on using inactivated bacteria to train the animal’s natural defenses, reducing both the incidence and severity of infections.
It aligns with current efforts to reduce antibiotic use in livestock and promote sustainable health strategies that don’t contribute to antimicrobial resistance.
Broader implications beyond swine
Although the study focuses on pigs, the concept of training the innate immune system is broadly applicable. In human medicine, environmental bacteria, BCG vaccination, and fungal extracts have all been studied as tools to prime innate immunity against viral reinfections, including SARS-CoV-2.
This work reinforces the role of pigs as valuable translational models in immunology and supports a paradigm shift: using the microbiota not just as something to monitor, but as a potential source of beneficial immune signals.
Study reference:
Tort-Miró, A., Alonso, U., Martín-Mur, B., Muñoz-Basagoiti, J., Zeng, Y., Marín-Moraleda, D., Ezcurra, E., Montaner-Tarbes, S., Navas, M.J., Muñoz, M., Monleón, P., González-Oliver, J., Cano, E., Vilalta, C., Caballé, M., Criado, L., Kochanowski, K., Accensi, F., Aragón, V., Correa-Fiz, F., Esteve-Codina, A., Rodríguez, F., & Argilaguet, J. (2025). Inactivated Rothia nasimurium promotes a persistent antiviral immune status in porcine alveolar macrophages. Frontiers in Immunology, 16:1584092. https://doi.org/10.3389/fimmu.2025.1584092
