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Research Article: Neonatal CD19 + B220 lo cells sense microbiota via TLR2/4 activation driving proliferation and differentiation

Date Published: 2026-06-19

Abstract:
Neonatal respiratory infections remain a leading cause of mortality and morbidity worldwide, yet there is still little information about the role of B cell populations in the respiratory tract. CD19 + B220 lo are B cells that are found in neonatal lungs, and antibiotic treatment of pregnant females and their offspring reduced the number of these cells and modified their VH immunoglobulin repertoire. Activation in vitro by the TLR2 (PAM3 and FSL1) and TLR4 (LPS) ligands induced proliferation and differentiation of neonatal B cells in the lung and spleen, generating CD138 + cells and releasing IgM, IgG1 and small amounts of IgA, as well as several cytokines. A higher frequency of CD138 + cells was observed within both purified CD19 + B220 lo and CD19 + B220 hi populations following in vitro TLR2/TLR1 stimulation with PAM3. The lung cultures adopted an inflammatory cytokine profile (TNF-?, IL1-?, IL6), as opposed to the regulatory profile (IL10) of spleen cultures. Taken together, these findings support the conclusion that neonatal lung and spleen CD19 + B220 lo cells can sense the microbiota via both TLR2 and TLR4, thereby promoting their activation and differentiation.

Introduction:
The lung is an organ specialized in gas exchange that is a target for many pathogens and environmental insults. Its role as a defensive barrier is highly important since the respiratory epithelium, with the mucus and the antimicrobial molecules (including peptides and surfactant proteins), acts as a physical barrier while allowing gas exchange ( 1 , 2 ). During neonatal life the lung is also an organ in which early immune responses are shaped by the first microbial and environmental exposures, making the study of…

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