Role of Tocilizumab in Down Regulating sCD163 Plasmatic Levels in a Cohort of COVID-19 Patients

Abstract

Background: CD163, a haptoglobin-hemoglobin scavenger receptor mostly expressed by monocytes and macrophages, is involved in the regulation of inflammatory processes. Following proteolytic cleavage after pro-inflammatory stimulation, CD163 is shed from the cell surface and its soluble form in plasma, sCD163, is a biomarker of monocyte/macrophage lineage activation.The assessment of sCD163 plasmatic levels in an early stage of the disease could have clinical utility in predicting the severity of COVID-19 pneumonia. The use of tocilizumab (monoclonal antibody anti-IL-6 receptor) in COVID-19 patients reduces lethality rate at 30 days. The aim of the study was to investigate the effect of tocilizumab on sCD163 plasmatic levels in a cohort of COVID-19 patients.

Methods: In COVID-19 patients, on hospital admission (T0), after 7 days from hospitalization (T7) and after 45 days from discharge (T45) sCD163 plasmatic levels were evaluated, along with other laboratory parameters. COVID-19 patients were stratified into tocilizumab (TCZ) and non-tocilizumab (non-TCZ) groups. TCZ group was further divided into responder (R) and non-responder (NR) groups. Patients who died or required mechanical ventilation were defined as NR. As control group, healthy donors (HD) were enrolled.

Results: Seventy COVID-19 patients and 47 HD were enrolled. At T0, sCD163 plasmatic levels were higher in COVID-19 patients compared to HD (p<0.0001) and the longitudinal evaluation showed a reduction in sCD163 plasmatic levels at T7 compared to T0 (p=0.0211). At T0, both TCZ and non-TCZ groups showed higher sCD163 plasmatic levels compared to HD (p<0.0001 and p=0.0147, respectively). At T7, the longitudinal evaluation showed a significant reduction in sCD163 plasmatic levels (p=0.0030) only in the TCZ group, reaching levels comparable to those of HD. Conversely, not statistically significance in non-TCZ group was observed and, at T7, a statistically significance was found comparing non-TCZ group to HD (p=0.0019). At T0, R and NR groups showed not statistically significance in sCD163 plasmatic levels and both groups showed higher levels compared to HD (p=0.0001 and p=0.0340, respectively). The longitudinal evaluation showed significant reductions in both groups (R: p=0.0356; NR: p=0.0273) independently of the outcome. After 45 days of follow-up sCD163 plasmatic levels remain stable.

Conclusion: sCD163 plasmatic levels are increased in COVID-19 pneumonia and is efficiently down-regulated by tocilizumab treatment regardless of the clinical outcome.

Keywords: ELISA; IL-6; SARS-CoV-2; monocytes/macrophages; sCD163; tocilizumab.

Figure 1

Evaluation of sCD163 plasmatic levels and correlations with clinical data. (A) sCD163 plasmatic levels were evaluated in 70 COVID-19 patients and 47 HD. The differences were evaluated using the nonparametric Mann-Whitney test. Data are shown as median (lines). (B) sCD163 plasmatic levels were evaluated in 34 patients with ARDS (ARDS group) and 36 patients without ARDS (non-ARDS group) using the nonparametric Mann-Whitney test. Both ARDS and non-ARDS groups were compared to HD using the nonparametric Kruskal-Wallis test with Dunn’s post-test. Data are shown as median (lines). (C) sCD163 plasmatic levels were longitudinal evaluated in 70 COVID-19 patients at two time-points: at T0 (on hospital admission) and T7 (after seven days from hospital admission) using Wilcoxon test. Both T0 and T7 were compared to HD using the nonparametric Kruskal-Wallis test with Dunn’s post-test. Data are shown as median (lines). (D) Positive correlation between sCD163 plasmatic levels and absolute neutrophil count on 70 COVID-19 patients. Linear correlation was evaluated by using the regression test, R² = 0.0696, p=0.0273. (E) Negative correlation between sCD163 plasmatic levels and absolute lymphocytes count on 70 COVID-19 patients. Linear correlation was evaluated by using the regression test, R² = 0.0702, p=0.0290. (F) Positive correlation between sCD163 plasmatic levels and neutrophil/lymphocyte ratio (NLR) on 70 COVID-19 patients. Linear correlation was evaluated by using the regression test, R² = 0.0843 p=0.0171. All correlations were performed using Spearman test. Spearman coefficient (ρ) and statistical significance (p) are reported in the graphics. **** p> 0.0001; **0.01 < p < 0.001; *0.05 < p <0.01.

Figure 2

Evaluation of sCD163 plasmatic levels in tocilizumab and non-tocilizumab groups. (A) sCD163 plasmatic levels were evaluated in 45 tocilizumab treated patients (TCZ) and 25 tocilizumab untreated patients (non-TCZ). The differences were evaluated using the nonparametric Mann-Whitney test. Data are shown as median (lines). Both TCZ and non-TCZ groups were compared to HD using the nonparametric Kruskal-Wallis test with Dunn’s post-test. Data are shown as median (lines). (B) sCD163 plasmatic levels were evaluated in tocilizumab treated (TCZ) and tocilizumab untreated (non-TCZ) patients stratified according to the development of ARDS. The differences were evaluated using the nonparametric Mann-Whitney test. Data are shown as median (lines). (C) sCD163 plasmatic levels were longitudinal evaluated in 45 tocilizumab treated patients at two time-points: at T0 (on hospital admission) and T7 (after seven days from hospital admission) using Wilcoxon test. Both T0 and T7 were compared to HD using the nonparametric Kruskal-Wallis test with Dunn’s post-test. Data are shown as median (lines). (D) sCD163 plasmatic levels were longitudinal evaluated in 25 tocilizumab treated patients at two time-points: at T0 (on hospital admission) and T7 (after seven days from hospital admission) using Wilcoxon test. Both T0 and T7 were compared to HD using the nonparametric Kruskal-Wallis test with Dunn’s post-test. Data are shown as median (lines). ****p > 0.0001; **0.01 < p < 0.001; *0.05 < p <0.01.

Figure 3

Evaluation of sCD163 plasmatic levels according to response to tocilizumab treatment. (A) sCD163 plasmatic levels were evaluated in 35 responder (R) and 10 non-responder (NR) patients. The differences were evaluated using the nonparametric Mann-Whitney test. Data are shown as median (lines). Both R and NR groups were compared to HD using the nonparametric Kruskal-Wallis test with Dunn’s post-test. Data are shown as median (lines). (B) sCD163 plasmatic levels were longitudinal evaluated in 35 responder (R) patients at two time-points: at T0 (on hospital admission) and T7 (after seven days from hospital admission) using Wilcoxon test. Both T0 and T7 were compared to HD using the nonparametric Kruskal-Wallis test with Dunn’s post-test. Data are shown as median (lines). (C) sCD163 plasmatic levels were longitudinal evaluated in 10 non-responder (NR) patients at two time-points: at T0 (on hospital admission) and T7 (after seven days from hospital admission) using Wilcoxon test. Both T0 and T7 were compared to HD using the nonparametric Kruskal-Wallis test with Dunn’s post-test. Data are shown as median (lines). (D) sCD163 plasmatic levels were longitudinal evaluated in 22 responder (R) patients at three time-points: at T0 (on hospital admission), T7 (after seven days from hospital admission) and T45 (30-45 days from discharge) using Friedman test with Dunn’s post-test. Each time-point (T0, T7 and T45) was compared to HD using the nonparametric Kruskal-Wallis test with Dunn’s post-test. Data are shown as median (lines). ***0.0001<p<0.001; *0.01<p<0.05.