Abstract Body: Introduction
In this study, we investigated peripheral blood mononuclear cells (PBMCs) transcriptomics of patients who had a stroke using single-cell RNA sequencing (scRNA-seq) to understand peripheral immune response after Early neurological deterioration (END) based on the gene expression in an unbiased way.

Methods
Transcriptomes of PBMCs from 5 patients who had END within 24 hours after stroke onset were compared with 5 race-matched/age- matched/gender-matched controls. Based on whether the patient experienced END and the timing before and after the occurrence of END, the samples were divided into four groups: END_T0, END_T1, Non-END_T0, and Non-END_T1.

Results
A total of 20 peripheral blood PBMC samples were collected from patients with acute ischemic stroke before and after the occurrence of END. Compared with Non-END, the proportion of mononuclear macrophages in the peripheral blood of patients with END and the number of differential genes have significantly increased (P < 0.05). Further heterogeneity analysis of mononuclear macrophages revealed a cell subset C1Q⁺ Mono that highly expresses C1QA. The proportion of this subset significantly increased before and after the occurrence of END (P < 0.05). Pseudotime analysis showed that its differentiation trajectory is different from that of classical mononuclear macrophages, and functional enrichment suggests it is related to the activation of inflammatory cells and the coagulation system.

Conclusion
For the first time, our study constructed a peripheral blood immune landscape of acute ischemic stroke before and after the occurrence of END, as well as in Non-END cases, based on scRNA-seq. our study also identified a novel monocyte subpopulation, providing new insights into the immune regulation of END