# In ovo carvacrol enriched inflammatory and T-cell transcriptional responses to Escherichia coli LPS in broiler chickens

## TL;DR

Injecting carvacrol into chicken eggs may boost immune responses to E. coli LPS by affecting T-cell and inflammatory genes.

## Contribution

This study shows in ovo carvacrol modulates immune gene responses to E. coli LPS in chickens.

## Key findings

- LPS challenge reduced chicken weight gain and increased spleen weight.
- Carvacrol enriched inflammatory and T-cell pathways during LPS challenge.
- Carvacrol upregulated cytokine and chemokine genes in response to LPS.

## Abstract

Enhancing immune responsiveness against pathogens is crucial for maintaining health. In broiler chickens, the in ovo delivery of carvacrol, a phenolic compound found in oregano and thyme, has shown promising immunomodulatory activity. This study investigated the hypothesis that the in ovo delivery of carvacrol would regulate the immune response against Escherichia coli lipopolysaccharide (LPS) in broiler chickens.

In ovo carvacrol (injected at embryonic day 17.5) and/or E. coli LPS challenge (repeated intraperitoneal injections at post-hatching d7 and d14) were tested in a 2 × 2 factorial arrangement, resulting in four groups: 1) in ovo saline without challenge (saline), 2) in ovo saline with LPS challenge, 3) in ovo carvacrol without challenge, and 4) in ovo carvacrol with LPS challenge. Performance parameters were collected, and relative organ weights were measured at d14. Splenic samples were collected 6 h after the second challenge (d14) and used for transcriptomic analyses.

The LPS challenge resulted in lower chicken weight gain and higher relative spleen weight. The in ovo delivery of carvacrol had no impact on these measures. The transcriptomic comparisons for the effects of LPS challenge identified 786 differentially expressed genes (DEGs) between groups 2 and 1 (without in ovo carvacrol) and 1,832 DEGs between groups 4 and 3 (with in ovo carvacrol) [false discovery rate (FDR)< 0.05, −0.5 > logFC > 0.5], primarily enriching inflammatory pathways (p< 0.01). The transcriptomic comparisons for the effects of in ovo carvacrol identified 89 DEGs between groups 3 and 1 and 720 DEGs between 4 and 2 (p< 0.05, −0.5 > logFC > 0.5). Functional analyses (4 vs. 2) showed that the in ovo delivery of carvacrol enriched pathways that can be related to T-cell activation at 6 h after LPS challenge, mainly influenced by the upregulation of DEGs encoding for cytokines and chemokines (p< 0.01). Overall, these findings suggest that the in ovo delivery of carvacrol may modulate immune responses toward an E. coli LPS challenge, specifically by upregulating the gene expression of cytokines, chemokines, and their receptors, persisting until at least 14 days post-hatching.