Sepsis-induced long-term immune paralysis--results of a descriptive, explorative study

Abstract

Background: Long-lasting impairment of the immune system is believed to be the underlying reason for delayed deaths after surviving sepsis. We tested the hypothesis of persisting changes to the immune system in survivors of sepsis for the first time.

Methods: In our prospective, cross-sectional pilot study, eight former patients who survived catecholamine-dependent sepsis and eight control individuals matched for age, sex, diabetes and renal insufficiency were enrolled. Each participant completed a questionnaire concerning morbidities, medications and infection history. Peripheral blood was collected for determination of i) immune cell subsets (CD4(+), CD8(+) T cells; CD25(+) CD127(-) regulatory T cells; CD14(+) monocytes), ii) cell surface receptor expression (PD-1, BTLA, TLR2, TLR4, TLR5, Dectin-1, PD-1 L), iii) HLA-DR expression, and iv) cytokine secretion (IL-6, IL10, TNF-α, IFN-γ) of whole blood stimulated with either α-CD3/28, LPS or zymosan.

Results: After surviving sepsis, former patients presented with increased numbers of clinical apparent infections, including those typically associated with an impaired immune system. Standard inflammatory markers indicated a low-level inflammatory situation in former sepsis patients. CD8(+) cell surface receptor as well as monocytic HLA-DR density measurements showed no major differences between the groups, while CD4(+) T cells tended towards two opposed mechanisms of negative immune cell regulation via PD-1 and BTLA. Moreover, the post-sepsis group showed alterations in monocyte surface expression of distinct pattern recognition receptors; most pronouncedly seen in a decrease of TLR5 expression. Cytokine secretion in response to important activators of both the innate (LPS, zymosan) and the adaptive immune system (α-CD3/28) seemed to be weakened in former septic patients.

Conclusions: Cytokine secretion as a reaction to different activators of the immune system seemed to be comprehensively impaired in survivors of sepsis. Among others, this could be based on trends in the downregulation of distinct cell surface receptors. Based on our results, the conduct of larger validation studies seems feasible, aiming to characterize alterations and to find potential therapeutic targets to engage.

Keywords: Immune system; Immunocompromised; Immunology; Sepsis.

Figures

Fig. 1

Characterization of immune cells subsets. Peripheral blood was collected from eight survivors of sepsis and matched controls and analyzed by flow cytometry to determine the percentage of circulating CD4+ and CD8+ subsets of CD3+ T cells, the amount of regulatory T cells (CD25+ CD127- Treg) as a fraction of all CD4+ cells, and CD14+ monocytes of all leucocytes. The markers used are described in “Methods”. Each data point represents an individual patient. Horizontal lines indicate median values

Fig. 2

Determination of the pattern of expression of specific receptors on CD4+ and CD8+ T cells. Peripheral blood was collected from eight survivors of sepsis and matched controls and stained for the indicated markers, followed by determination of percent positive relative to isotype control staining (bottom line) and quantification of fluorescence intensity by molecules of equivalent soluble fluorochrome (MESF) calculation (upper line) as described in “Methods”. Each data point represents an individual patient. Horizontal lines indicate median values. PD programmed cell death, BTLA B- and T-lymphocyte attenuator

Fig. 3

Determination of expression pattern of specific receptors on monocytes. Peripheral blood was collected from eight survivors of sepsis and matched controls and stained for the indicated markers, followed by determination of percent positive relative to isotype control staining (bottom line) and quantification of fluorescence intensity by molecules of equivalent soluble fluorochrome (MESF) calculation (upper line) as described in “Methods”. Each data point represents an individual patient. Horizontal lines indicate median values. TLR toll-like receptor, PD-1 L programmed cell death ligand

Fig. 4

Determination of human leukocyte antigen (HLA)-DR expression on monocytes. Peripheral blood was collected from eight survivors of sepsis and matched controls and HLA-DR expression was measured. Each data point represents an individual patient. Horizontal lines indicate median values

Fig. 5

Cytokine secretion of ex-vivo-stimulated whole blood. Peripheral blood was collected from eight survivors of sepsis (S) and matched controls (C). Whole blood was stimulated with either CD3/28 antibody (α-CD3/28), lipopolysaccharide (LPS) or Zymosan. Supernatants were harvested after 24 h and TNF-α, interferon-γ (IFN-γ), and IL-6 and IL-10 were measured by enzyme-linked immunosorbent assay. Each data point represents an individual patient. Horizontal lines indicate median values. CD cluster of differentiation