The Lectin Complement Pathway in Patients with Necrotizing Soft Tissue Infection

Abstract

Background: Mannose-binding lectin (MBL) and ficolins are pattern recognition molecules (PRMs) that play an important role during infection through activation of the lectin complement pathway. We assessed whether plasma PRM levels were associated with mortality in patients with necrotizing soft tissue infection (NSTI).

Methods: We conducted a prospective, observational study over 25 months involving 135 NSTI patients with a maximum follow-up of 2.7 years. Blood samples were taken upon admission. Non-infected patients served as controls.

Results: PRM levels were significantly lower compared with controls. A baseline Ficolin-2 level below the median was associated with mortality at the end of follow-up (p = 0.007). No significant association was found for MBL, Ficolin-1 and Ficolin-3. A Ficolin-2 level below the median had a negative predictive value of 0.94 for 28-day mortality, and a level below the optimal cut-off was independently associated with 28-day mortality when adjusted for age, sex and chronicity [hazard ratio 6.27 (95% confidence interval 2.28-17.21), p < 0.0001], also when Simplified Acute Physiology Score II was included in the analysis [hazard ratio 3.16 (95% confidence interval 1.03-9.73), p = 0.045].

Conclusions: All PRMs were significantly lower in patients with NSTI than in controls. Only baseline Ficolin-2 was associated with short- and long-term mortality. A high baseline Ficolin-2 level indicated a 94% chance of surviving the first 28 days after admission.

Fig. 1

Levels of PRMs upon admission (baseline) and on the following days in patients with NSTI and in non-infected control patients. Values denote medians with IQR. Differences were analyzed with the Mann-Whitney U test. Microtiter plates were coated with monoclonal antibodies against Ficolin-1, Ficolin-2, Ficolin-3 and MBL. EDTA plasma samples were diluted in phosphate-buffered saline with 0.05% Tween (Ficolin-1 1:100, Ficolin-2 1:300, Ficolin-3 1:500, MBL 1:300).

Fig. 2

Residual activation capacity of the complement system in patients with NSTI and in non-infected control patients. Values denote medians with IQR. Differences were analyzed with the Mann-Whitney U test. Assessment of classical pathway activity was performed on anti-human albumin/albumin immune complexes (plasma samples diluted 1:400), ficolin-mediated lectin pathway activity on acetylated BSA (plasma samples diluted 1:1,000) and alternative pathway activity on lipopolysaccharide (plasma samples diluted 1:10).

Fig. 3

Kaplan-Meier curves of long-term mortality up to 2.7 years in patients with NSTI stratified by median level of MBL (≤627.3 ng/ml), Ficolin-1 (≤322.3 ng/ml), Ficolin-2 (≤2.9 µg/ml) and Ficolin-3 (≤15.0 µg/ml). Differences were assessed by the log-rank test.

Fig. 4

ROC curve of 28-day mortality in patients with NSTI according to the baseline level of the lectin markers.

Fig. 5

Residual activation capacity of the complement system in patients with NSTI according to 28-day mortality. Values denote medians with IQR. Differences were analyzed with the Mann-Whitney U test. Assessment of classical pathway activity was performed on anti-human albumin/albumin immune complexes (plasma samples diluted 1:400), ficolin-mediated lectin pathway activity on acetylated BSA (plasma samples diluted 1:1,000) and alternative pathway activity on lipopolysaccharide (plasma samples diluted 1:10).