# Embryonic thermal manipulation enhances splenic immunity and regulates inflammatory responses to Escherichia coli in broiler chickens

## TL;DR

Heating chicken embryos during development improves their immune response and reduces inflammation when infected with E. coli.

## Contribution

This study shows that embryonic thermal manipulation modulates immune responses and reduces inflammation in broiler chickens after E. coli infection.

## Key findings

- Embryonic thermal manipulation downregulates pro-inflammatory genes like iNOS and TNF-α after E. coli infection.
- Thermal manipulation increases IgA levels and reduces serum AGP, indicating better immune regulation and less inflammation.
- TM upregulates TGF-β, suggesting a shift toward immunoregulation rather than excessive inflammation.

## Abstract

Escherichia coli (E. coli) infections continue to pose a significant health and economic burden to the poultry industry, with increasing restrictions on antibiotic use underscoring the need for alternative strategies to improve host resilience. Thermal manipulation (TM) during embryogenesis has been proposed as an economical strategy to enhance thermotolerance, stress resilience, and immune functionality in broilers. This study aimed to investigate the effect of TM during embryonic development on the immune response of broiler chickens following an E. coli challenge.

A total of 740 Ross broiler eggs were assigned to either a control incubation (37.8 °C, 56% RH) or TM (39 °C and 65% RH for 18 h daily, on embryonic days 10–18). After hatching, chicks were subdivided into saline- or E. coli-injected groups. Splenic expression of pro-inflammatory mediators (iNOS and TNF-α), signaling receptors (NF-κB, p65, TLR-2, and TLR-4), and immunoregulatory cytokine (TGF-β) was quantified by RT-qPCR. At the same time, serum levels of acute-phase proteins (α1-acid glycoprotein (AGP) and C3) and total circulating immunoglobulins (IgA, IgM, and IgY) were assessed by ELISA.

TM significantly modulated post-challenge immune responses, including downregulation of iNOS, TNF-α, NF-κB, TLR-2, and TLR-4, and upregulation of TGF-β. Notably, TM was associated with a stronger and more sustained circulating IgA response after infection. Additionally, TM lowered serum AGP levels under the E. coli challenge, which indicates reduced systemic inflammation.

These findings show that embryonic TM boosts both splenic and systemic immune regulation while reducing excessive inflammatory responses to bacterial challenges in broilers.