The innate immune response to lower respiratory tract E. Coli infection and the role of the CCL2-CCR2 axis in neonatal mice

Abstract

Neonates have greater morbidity/mortality from lower respiratory tract infections (LRTI) compared to older children. Lack of conditioning of the pulmonary immune system due to limited environmental exposures and/or infectious challenges likely contributes to the increase susceptibility in the neonate. In this study, we sought to gain insights into the nature and dynamics of the neonatal pulmonary immune response to LRTI using a murine model. Methods Wildtype (WT) and Ccr2−/− C57BL/6 neonatal and juvenile mice received E. coli or PBS by direct pharyngeal aspiration. Flow cytometry was used to measure immune cell dynamics and identify cytokine-producing cells. Real-time PCR and ELISA were used to measure cytokine/chemokine expression. Results Innate immune cell recruitment in response to E. coli-induced LRTI was delayed in the neonatal lung compared to juvenile lung. Lung clearance of bacteria was also significantly delayed in the neonate. Ccr2−/− neonates, which lack an intact CCL2-CCR2 axis, had higher mortality after E. coli challenged than Ccr2+/+ neonates. A greater percentage of CD8+ T cells and monocytes from WT neonates challenged with E. coli produced TNF compared to controls. Conclusion The pulmonary immune response to E. coli-induced LRTI differed significantly between neonatal and juvenile mice. Neonates were more susceptible to increasing doses of E. coli and exhibited greater mortality than juveniles. In the absence of an intact CCL2-CCR2 axis, susceptibility to LRTI-induced mortality was further increased in neonatal mice. Taken together these findings underscore the importance of age-related differences in the innate immune response to LRTI during early stages of postnatal life.

DNA methylation regulates the neonatal CD4+ T-cell response to pneumonia in mice

“…The juvenile CD4 + T-cell response to early infection-and inflammation-induced acute lung injury involves coordination of multiple T-cell subsets including Th1, Th2, Th17, and Treg cells (14,15,17,18,30). We elected to isolate bulk unfractionated CD4 + T-cells for our studies in order to provide a broad view of the CD4 + T-cell transcriptional and epigenetic landscape.…”

“…Neonatal (3-4-day-old) and juvenile (11-14-day-old) mice were randomized by cage to receive either PBS alone or E. coli in PBS (2.8 x 10 6 colony-forming units). Forceps were used to gently retract the tongue, liquid was deposited in the pharynx, and aspiration of fluid was directly visualized as previously described (18). Neonatal mice were aspirated with 10 µL of fluid and juvenile mice received 15 µL of fluid.…”

“…Because of previous work demonstrating the hypofunctional lung CD4 + T-cell response to neonatal early LRTI (17,18), we performed comprehensive transcriptional profiling with RNA-sequencing (RNA-seq) on sorted lung CD4 + T-cells from neonates and juveniles exposed to either PBS or E. coli via aspiration 48 hours previously. Multiple group testing with a false discovery rate (FDR) q-value ≤ 0.05 revealed 3,932 differentially expressed genes (DEGs).…”

“…Additionally, experimental data show that CD4 + T-cell subsets increase in the lungs of both neonatal and juvenile mice within 48 hours after aspiration of Escherichia coli bacteria (18). A detailed understanding of the CD4 + T-cell response to LRTI as a function of age among pediatric populations remains unknown.…”

A potent myeloid response is rapidly activated in the lungs of premature Rhesus macaques exposed to intra-uterine inflammation

“…in [38][39][40] ). Described defects notably include the decreased recruitment of neutrophils and inflammatory monocytes into the lung in response to E. coli instillation during the same time period, compared to juvenile mice 41 . In contrast, our data in a NHP model argue that fetal neutrophils and inflammatory monocytes can quickly migrate into the pulmonary environment, as these two populations became very abundant in the lung 16hrs after IA LPS.…”