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Microbes & Immunity Understanding lung development, health, and diseases

levels, a marker of intestinal inflammation, in both children morbidity and death rates. The lung microbiota, as well
and adults with CF. However, probiotics did not appear to as the gut microbiota, play a crucial role in the infection
influence the rate of pulmonary exacerbations and were process. The lung microbiomes of COVID-19 patients
74
sometimes associated with side effects such as vomiting, differ markedly from those of healthy individuals.
diarrhea, or allergic reactions. The researchers conclude Elevated levels of Acinetobacter, Chryseobacterium,
that while probiotics may offer potential benefits for CF Burkholderia, Brevundimonas, Sphingobium, and members
patients, further research and validation are necessary to of the Enterobacteriaceae family have been observed in the
confirm these findings. 69 lungs of affected patients. In addition, microbial species
can be identified through the 16S rRNA sequencing to
6.2.4. IPF analyze BALF samples from COVID-19 patients. Missing
The development and progression of IPF have been linked microorganisms can be injected into the lungs to promote
to changes in lung microbiota and bacterial infections. local immunity and boost the immune response. 75
Patients with IPF have a higher bacterial load in their
bronchoalveolar lavage fluid (BALF) compared to healthy 6.2.6. Influenza
controls, with an increased prevalence of Streptococcus, Influenza is a viral illness that remains a major concern for
Pneumococcus, and Staphylococcus species. IPF is a public health officials worldwide. Although vaccination
rapidly progressing chronic lung disease characterized by is used to prevent the disease, its efficacy is restricted due
a progressive decline in lung function and an unknown to rapid viral mutagenesis. As a result, boosting natural
etiology. 70,71 defenses by stimulating cellular immunity may serve as
an effective method to combat influenza. Lactobacilli
Studies have found that bacteria present in the BALF
of newly diagnosed IPF patients, with a loss of lung strains, such as Lactobacillus casei Shirota, have been
demonstrated to activate lung natural killer cells, resulting
microbiome diversity, correlates with the progression of in greater cytotoxic activity and higher levels of IL-1β,
the disease. This decline in diversity is linked to a decrease tumor necrosis factor (TNF), and MCP-1 mRNA in lung
in Proteobacteria and an increase in Firmicutes and 76
Bacteroidetes, including families such as Streptococcaceae, cells from probiotic-treated mice.
Veillonellaceae, and Prevotellaceae. Moreover, these In a different study, mice infected with influenza viruses
microbial changes are linked to important indicators of (PR8 and H1N1) had a substantially lower viral titter in
IPF, including decreased 6-min walk distance, decreased their nasal wash fluid than those not receiving probiotics.
forced vital capacity, and elevated serum levels of lactate After intranasal probiotic administration, mediastinal
dehydrogenase and surfactant protein D. Although this lymph nodes were removed, and the node cells were
study did not include healthy controls, prior research cultivated with and without PR8 exposure. Interestingly,
has suggested a decrease in microbiome diversity in IPF these cells produced cytokines such as IL-12, IFN-γ, and
patients compared to healthy individuals. 72 TNF-α, similar to what was observed during in vivo viral
infection. Notably, Lactobacillus casei Shirota, a bacterium
6.2.5. COVID-19 used in fermented milk production, has demonstrated
Healthy gut microbiota can increase the number of CD8 both safety and efficacy in combating respiratory tract
+
T cells and enhance the antiviral response in the lungs, infections when applied as an aerosol or spray. 77,78
potentially affecting the severity and clinical symptoms The onset and course of chronic lung illnesses are
of the virus. Studies on COVID-19 patients have revealed influenced by the lung microbiome. However, several
significant changes in gut microbiota composition, questions remain unresolved, such as the reasons behind
including a decrease in beneficial bacteria and an increase microbiota variation in chronic lung disorders and whether
in opportunistic pathogens. Moreover, oral administration these alterations are a result of or a cause of the illness.
of Lactobacillus has been found to increase serum vitamin
D levels, which may mitigate the severity of COVID-19 7. Discussion
through immunomodulatory effects and inhibition of Lung development is a highly regulated process that involves
cytokine storms. 73 six major stages such as embryonic, pseudoglandular,
Probiotics may also interfere with SARS-CoV-2 by canalicular, saccular, alveolar, and microvascular, with
blocking its major receptor, angiotensin-converting each stage governed by intricate signaling pathways.
enzyme 2, through the release of peptides with high binding These pathways drive cellular differentiation and tissue
affinity. This relationship is crucial for the progression of morphogenesis, ensuring the lungs’ structural and
the illness. Therefore, probiotics may help lower COVID-19 functional maturation. Understanding these mechanisms
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Volume 2 Issue 3 (2025) 54 doi: 10.36922/mi.7719