Integrated Single-Cell and Bulk Transcriptomics Unveils Immune Profiles in Chick Erythroid Cells upon Avian Pathogenic Escherichia coli Infection

Nucleated erythroid cells (NECs) have emerged as active participants in immune responses in addition to their canonical oxygen transport function. The subpopulations and immune heterogeneity of chick erythroid cells (ch-ECs) upon infection have not been fully characterized. Single-cell RNA sequencing (scRNA-seq) was used to profile ch-ECs in chicks infected with avian pathogenic <i>Escherichia coli</i> (APEC). Unsupervised clustering uncovered ten distinct ch-EC subpopulations (C1-C10), with significant compositional shifts between infected and control groups. Pseudotime analysis revealed a developmental continuum: C1, C3, C5, and C9 as early progenitors; C2, C4, C6, C7, and C10 as mature erythroid cells; and C8 as a naive population. We revealed 62 immune-related genes, including protein kinases and heat shock proteins, and subpopulation-specific differentially expressed genes (DEGs) linked to immune functions. SCENIC analysis revealed Fos, Srf, and Stat3 as key transcription factors with elevated regulon activity and specificity following infection. Subpopulations C2, C4, C6, and C7, which exhibited marked abundance changes, were scrutinized for immune relevance through integrated multi-omics analysis. Immune-related genes including <i>FOS</i>, <i>AKAP9</i>, <i>HS6ST1</i>, <i>GAB3</i>, <i>TFRC</i>, <i>HSPA8</i>, <i>HSP90AA1</i>, and <i>DNAJB6</i> were identified. Enrichment analysis indicated activation of the MHC class I antigen presentation pathway, while pathways such as Mitogen-Activated Protein Kinase (MAPK) signaling, NOD-like receptor (NLR) signaling, and the heat shock response were found to be suppressed. In conclusion, this study delineates the immune gene repertoire and signaling networks of ch-ECs during APEC infection, offering new perspectives on NEC immunoregulatory functions.