Abstract
BACKGROUND: Clinical flow cytometry has revealed that sepsis elicits a multifaceted and time-dependent immune response characterized by the simultaneous activation of pro- and anti-inflammatory pathways. This technology has enabled the identification of immune dysfunction patterns and the development of immunostimulatory approaches, thereby offering new insights into sepsis pathophysiology and allowing for a refined delineation of immune trajectories in affected patients. METHODS: Whole-blood samples were obtained from patients presenting to the emergency department (ER) with clinical features of sepsis or septic shock (Figure 1). Based on blood culture results, patients were classified into confirmed sepsis (c-SEP) or no sepsis (n-SEP) groups. Flow-cytometric immunophenotyping was performed to investigate the percentage of subpopulations of innate (monocytes, neutrophils, dendritic cells) and adaptive (T-cell) immune cell subsets (Figure 1). Age- and sex-matched healthy donors (HDs) served as controls. RESULTS: A total of 42 patients (22 c-SEP, 20 n-SEP) and 12 HDs were enrolled. Among c-SEP cases, 68% (15/22) were positive for Gram- negative pathogens, with Escherichia coli being the most common isolate (32% [7/22]). Compared with HDs, patients demonstrated increased immature neutrophils (P= 0.0193) and decreased plasmacytoid dendritic cells (P= 0.0153) (Table 1, Figure 2). Significant reductions in CD3⁺ (P= 0.0013) and CD4⁺ T cells (P= 0.0083), but not CD8⁺ T cells, were observed (Table 1, Figure 2). Within the CD8⁺ compartment, naïve (P= 0.0232) and central memory cells (P= 0.0002) were reduced, whereas senescent (P= 0.0498), effector (P= 0.0027) and effector memory (P= 0.0304) subsets were increased (Table 1, Figure 2). When stratified by microbiological results, n-SEP and c-SEP patients shared similar immunological trends. However, the increase in immature neutrophils (P= 0.0031) and reduction in CD8⁺ naïve T cells (P= 0.0249) were significant only in n-SEP, while plasmacytoid dendritic cells reduction (P= 0.0367) remained specific to c-SEP (Table 2, Figure 2). Indeed, immature neutrophils were significantly higher in n-SEP than in c-SEP (P= 0.0258) (Table 2, Figure 2). Moreover, naïve CD4⁺ T cells were significantly increased in c-SEP patients (P= 0.0036), whereas effector memory CD4⁺ T cells (P= 0.0492) were reduced in this group when compared to n-SEP (Table 2, Figure 2). CONCLUSIONS: In conclusion, the present findings suggest that sepsis may induce immune dysregulation, as evidenced by skewed myeloid and T-cell subpopulations. This indicates concomitant immunoparalysis and inflammation, which are likely driven by persistent activation, tolerance mechanisms, and cellular depletion. These results highlight the importance of targeted immunomodulatory strategies for patients with sepsis. [Figure: see text] [Figure: see text] [Table: see text] [Table: see text]