Escherichia coli-induced inflammatory responses are temperature-dependent in human whole blood ex vivo.

Systemic inflammatory conditions are often associated with hypothermia or hyperthermia. Therapeutic hypothermia is used in post-cardiac arrest and some other acute diseases. There is a need for more knowledge concerning the effect of various temperatures on the acute inflammatory response. The complement system plays a crucial role in initiating the inflammatory response. We hypothesized that temperatures above and below the physiologic 37 °C affect complement activation and cytokine production ex vivo. Lepirudin-anticoagulated human whole blood from 10 healthy donors was incubated in the presence or absence of Escherichia coli at different temperatures (4 °C, 12 °C, 20 °C, 33 °C, 37 °C, 39 °C, and 41 °C). Complement activation was assessed by the terminal C5b-9 complement complex (TCC) and the alternative convertase C3bBbP using ELISA. Cytokines were measured using a 27-plex assay. Granulocyte and monocyte activation was evaluated by CD11b surface expression using flow cytometry. A consistent increase in complement activation was observed with rising temperature, reaching a maximum at 41 °C, both in the absence (C3bBbP p < 0.05) and presence (C3bBbP p < 0.05 and TCC p < 0.05) of E. coli. Temperature alone did not affect cytokine production, whereas incubation with E. coli significantly increased cytokine levels of IL-1ß, IL-2, IL-6, IL-8, IFN-γ, and TNF at temperatures > 20 °C. Maximum increase occurred at 39 °C. However, a consistent decrease was observed at 41 °C, significant for IL-1ß (p = 0.003). Granulocyte CD11b displayed the same temperature-dependent pattern as cytokines, with a corresponding increase in endothelial cell apoptosis and necrosis. Thus, blood temperature differentially determines the degree of complement activation and cytokine release.

Synthetic Oligodeoxynucleotide CpG Motifs Activate Human Complement through Their Backbone Structure and Induce Complement-Dependent Cytokine Release.

Bacterial and mitochondrial DNA, sharing an evolutionary origin, act as danger-associated molecular patterns in infectious and sterile inflammation. They both contain immunomodulatory CpG motifs. Interactions between CpG motifs and the complement system are sparsely described, and mechanisms of complement activation by CpG remain unclear. Lepirudin-anticoagulated human whole blood and plasma were incubated with increasing concentrations of three classes of synthetic CpGs: CpG-A, -B, and -C oligodeoxynucleotides and their GpC sequence controls. Complement activation products were analyzed by immunoassays. Cytokine levels were determined via 27-plex beads-based immunoassay, and CpG interactions with individual complement proteins were evaluated using magnetic beads coated with CpG-B. In whole blood and plasma, CpG-B and CpG-C (p < 0.05 for both), but not CpG-A (p > 0.8 for all), led to time- and dose-dependent increase of soluble C5b-9, the alternative complement convertase C3bBbP, and the C3 cleavage product C3bc. GpC-A, -B, and -C changed soluble fluid-phase C5b-9, C3bBbP, and C3bc to the same extent as CpG-A, -B, and -C, indicating a DNA backbone-dependent effect. Dose-dependent CpG-B binding was found to C1q (r = 0.83; p = 0.006) and factor H (r = 0.93; p < 0.001). The stimulatory complement effect was partly preserved in C2-deficient plasma and completely preserved in MASP-2-deficient serum. CpG-B increased levels of IL-1ß, IL-2, IL-6, IL-8, MCP-1, and TNF in whole blood, which were completely abolished by inhibition of C5 and C5aR1 (p < 0.05 for all). In conclusion, synthetic analogs of bacterial and mitochondrial DNA activate the complement system via the DNA backbone. We suggest that CpG-B interacts directly with classical and alternative pathway components, resulting in complement-C5aR1-dependent cytokine release.

Systemic complement activation is associated with respiratory failure in COVID-19 hospitalized patients.

Respiratory failure in the acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic is hypothesized to be driven by an overreacting innate immune response, where the complement system is a key player. In this prospective cohort study of 39 hospitalized coronavirus disease COVID-19 patients, we describe systemic complement activation and its association with development of respiratory failure. Clinical data and biological samples were obtained at admission, days 3 to 5, and days 7 to 10. Respiratory failure was defined as PO2/FiO2 ratio of ≤40 kPa. Complement activation products covering the classical/lectin (C4d), alternative (C3bBbP) and common pathway (C3bc, C5a, and sC5b-9), the lectin pathway recognition molecule MBL, and antibody serology were analyzed by enzyme-immunoassays; viral load by PCR. Controls comprised healthy blood donors. Consistently increased systemic complement activation was observed in the majority of COVID-19 patients during hospital stay. At admission, sC5b-9 and C4d were significantly higher in patients with than without respiratory failure (P = 0.008 and P = 0.034). Logistic regression showed increasing odds of respiratory failure with sC5b-9 (odds ratio 31.9, 95% CI 1.4 to 746, P = 0.03) and need for oxygen therapy with C4d (11.7, 1.1 to 130, P = 0.045). Admission sC5b-9 and C4d correlated significantly to ferritin (r = 0.64, P < 0.001; r = 0.69, P < 0.001). C4d, sC5b-9, and C5a correlated with antiviral antibodies, but not with viral load. Systemic complement activation is associated with respiratory failure in COVID-19 patients and provides a rationale for investigating complement inhibitors in future clinical trials.

Nodal metastasis in cervical cancer occurs in clearly delineated fields of immune suppression in the pelvic lymph catchment area.

In cervical cancer, high frequencies of regulatory T cells (Tregs) and immunosuppressive PD-L1+CD14+ antigen-presenting cells dominate the microenvironment of tumor-positive lymph nodes (LN+). It is unknown whether this is restricted to LN+ or precedes metastasis, emanating from the primary tumor and spreading through tumor-draining lymph nodes (TDLNs). To investigate immunosuppression in the lymphatic basin of cervical tumors, all dissected TDLNs of five cervical cancer patients (in total 9 LN+ and 74 tumor-negative lymph nodes (LN-)) were analyzed for FoxP3+ Tregs, CD8+ T cells, HLA-DR+- and PD-L1+ myeloid cells by immunohistochemistry.Tregs and PD-L1+ cells were found to form an immunosuppressive cordon around metastatic tumor cells. Importantly, whereas high HLA-DR+- and PD-L1+ cell rates were strongly associated with LN+, elevated Treg levels and decreased CD8+ T cell/Treg ratios were found similar in LN+ and adjacent LN-, as compared to LN- at more distant anatomical localizations. These data suggest that delineated fields of Treg-associated immune suppression in anatomically co-localized TDLNs enable metastasis by creating metastatic niches. This may be of importance for decision-making regarding (surgical) intervention in cervical cancer. Future efforts should include the implementation of immunotherapeutic regimens to overcome this immune suppression, establish loco-regional control and halt systemic tumor spread.