Dynamic trajectories of sepsis-induced immunoparalysis: from biological mechanisms to precision monitoring and targeted intervention

Sepsis is increasingly recognized as a heterogeneous syndrome in which profound immunosuppression, or immunoparalysis, may coexist with or follow the initial hyperinflammatory response. This state is characterized by impaired host responsiveness to pathogens and secondary immune stimuli and is associated with secondary infections, persistent organ dysfunction, and increased mortality. This narrative review summarizes the conceptual evolution and biological basis of sepsis-induced immunoparalysis, with particular emphasis on innate immune deactivation, adaptive immune dysfunction, immune-checkpoint upregulation, and metabolic-epigenetic reprogramming. A central focus is the transition from static, single-time-point assessment toward longitudinal characterization of immune trajectories. Current evidence suggests that the first 1–2 weeks after sepsis onset represent a critical period during which heterogeneous recovery patterns become apparent. Empirically supported patterns include improving or recovering immune states and persistent hyporesponsiveness, whereas fluctuating transitions remain a proposed, hypothesis-generating trajectory requiring further longitudinal validation. We review major monitoring indicators, including monocyte human leukocyte antigen-DR (mHLA-DR), absolute lymphocyte count (ALC), ex vivo cytokine production capacity, and immune checkpoints such as programmed death-1 (PD-1) and programmed death-ligand 1 (PD-L1). Importantly, most currently available biomarkers have stronger evidence for immune phenotyping and prognostic assessment than for predicting treatment response, and reported thresholds remain dependent on assay methodology, patient population, and measurement timing. We further discuss emerging biomarker-guided approaches, including the ImmunoSep trial, as early proof-of-concept for phenotype-enriched immunotherapy rather than definitive evidence for routine clinical implementation. Overall, repeated multi-marker assessment may improve characterization of immune trajectories and help identify candidate treatment-eligible windows; however, biomarker-based treatment thresholds, composite immune-clinical frameworks, and phenotype-matched immunotherapies require further prospective validation, particularly with respect to mortality, safety, and other patient-important outcomes.