# Nasal delivery of Lacticaseibacillus rhamnosus GG modulates respiratory immune responses and attenuates Mycoplasma pneumoniae pneumonia in a murine model

## TL;DR

Intranasal administration of LGG reduces lung inflammation and bacterial load in a mouse model of Mycoplasma pneumoniae pneumonia.

## Contribution

This study shows that intranasal LGG is safe and effective in both preventing and treating MPP in mice.

## Key findings

- Intranasal LGG reduces lung inflammation and pathogen load in MPP-infected mice.
- LGG promotes immune defenses through increased IgA, IgG, and anti-inflammatory cytokines.
- LGG suppresses pro-inflammatory cytokines and neutrophil levels in the lungs.

## Abstract

Mycoplasma pneumoniae pneumonia (MPP) management presents significant challenges due to the lack of an effective vaccine and the widespread occurrence of macrolide resistance. Recent studies investigating the use of oral or intranasal probiotics have shown promising results in reducing respiratory tract infections. In this study, BALB/c mice were initially given intranasal doses of Lacticaseibacillus rhamnosus GG (LGG), Limosilactobacillus reuteri F275, or a combination of these two strains, called MIX, to evaluate the safety of probiotic administration by examining lung tissue inflammation. Our results suggest that LGG is relatively safe, with minimal lung inflammatory responses, unlike the mild inflammation seen with L. reuteri F275 and MIX treatments. Next, LGG was administered to the mice via the respiratory tract on two consecutive days before or after infection with M. pneumoniae. The findings showed that both pre- and post-infection intranasal LGG significantly reduced lung inflammation caused by M. pneumoniae and decreased the pathogen load. The protective effects of nasal LGG delivery were associated with an increase in alveolar macrophages, higher levels of IgA in the bronchoalveolar lavage fluid (BALF), and increased IgG levels in the serum, all of which contribute to the elimination of the pathogen. Additionally, LGG pretreatment decreased neutrophil levels in the BALF and lungs, suppressed pro-inflammatory cytokines (tumor necrosis factor α, interleukin [IL]-6, and IL-17A), and boosted the production of the anti-inflammatory cytokine IL-10 in the BALF, reducing MPP severity. Intranasal administration of LGG appears to be a safe and potentially effective strategy for alleviating MPP in mouse models.

The increasing prevalence of antibiotic-resistant Mycoplasma pneumoniae pneumonia (MPP), together with the absence of an effective vaccine, highlights the critical demand for alternative therapeutic approaches. This study demonstrates that intranasal delivery of Lacticaseibacillus rhamnosus GG (LGG) significantly mitigates pulmonary inflammation and decreases bacterial load in a mouse model of MPP, both prophylactically and therapeutically. Notably, LGG strengthens essential immune defenses by promoting alveolar macrophage recruitment, increasing secretory IgA in the airways, and stimulating systemic IgG. It also modulates cytokine production, suppressing pro-inflammatory mediators while enhancing anti-inflammatory IL-10. These findings support intranasal LGG administration as a strategy with promising translational potential for MPP.