High interleukin-6 levels induced by COVID-19 pneumonia correlate with increased circulating follicular helper T cell frequency and strong neutralization antibody response in the acute phase of Omicron breakthrough infection

Abstract

Background: Acute immune responses to coronavirus disease 2019 (COVID-19) are influenced by variants, vaccination, and clinical severity. Thus, the outcome of these responses may differ between vaccinated and unvaccinated patients and those with and without COVID-19-related pneumonia. In this study, these differences during infection with the Omicron variant were investigated.

Methods: A total of 67 patients (including 47 vaccinated and 20 unvaccinated patients) who were hospitalized within 5 days after COVID-19 symptom onset were enrolled in this prospective observational study. Serum neutralizing activity was evaluated using a pseudotyped virus assay and serum cytokines and chemokines were measured. Circulating follicular helper T cell (cTfh) frequencies were evaluated using flow cytometry.

Results: Twenty-five patients developed COVID-19 pneumonia on hospitalization. Although the neutralizing activities against wild-type and Delta variants were higher in the vaccinated group, those against the Omicron variant as well as the frequency of developing pneumonia were comparable between the vaccinated and unvaccinated groups. IL-6 and CXCL10 levels were higher in patients with pneumonia than in those without it, regardless of their vaccination status. Neutralizing activity against the Omicron variant were higher in vaccinated patients with pneumonia than in those without it. Moreover, a distinctive correlation between neutralizing activity against Omicron, IL-6 levels, and cTfh proportions was observed only in vaccinated patients.

Conclusions: The present study demonstrates the existence of a characteristic relationship between neutralizing activity against Omicron, IL-6 levels, and cTfh proportions in Omicron breakthrough infection.

Keywords: Omicron; circulating follicular helper T cell; interleukin-6; neutralizing antibody; pneumonia.

Figure 1

Neutralization activity against the WT- and Omicron-derived variants, and anti-RBD antibody levels at hospital admission (within 5 days after symptom onset) in vaccinated (n = 47) and unvaccinated patients (n = 20). The Mann-Whitney test was used to compare values between vaccinated and unvaccinated patients. Each dot represents an individual value. Bars indicate medians with interquartile ranges. WT, wild-type; RBD, receptor-binding domain; ****P<0.0001; ns, not significant.

Figure 2

Neutralization activity against the WT- and Omicron-derived variants, and anti-RBD antibody levels at the acute phase of COVID-19, and associations with pneumonia or hypoxemic respiratory failure in vaccinated (n = 47) and unvaccinated patients (n = 20). The Mann-Whitney test was used to compare values between vaccinated patients with (n = 16) and without pneumonia (n = 31), vaccinated patients with (n = 7) and without hypoxemic respiratory failure (n = 40), unvaccinated patients with (n = 9) and without pneumonia (n = 11), and unvaccinated patients with (n = 2) and without hypoxemic respiratory failure (n = 18). Each level was measured at admission (within 5 days after symptom onset) and each dot represents an individual value. Bars indicate medians with interquartile ranges. WT, wild-type; RBD, receptor-binding domain; *P<0.05; **P<0.01; ns, not significant.

Figure 3

Relationship between serum levels of IL-6, CXCL10, LD and CRP, and pneumonia presence at the acute phase of COVID-19 in vaccinated (n = 47) and unvaccinated patients (n = 20). The Mann-Whitney test was used to compare values between vaccinated patients with (n = 16) and without pneumonia (n = 31), and unvaccinated patients with (n = 9) and without pneumonia (n = 11). Each level was measured at admission (within 5 days after symptom onset) and each dot represents an individual value. Bars indicate medians with interquartile ranges. IL, interleukin; CXCL10, C-X-C motif chemokine ligand 10; LD, lactate dehydrogenase; CRP, C-reactive protein; *P<0.05; **P<0.01; ***P<0.001; ****P<0.0001.

Figure 4

Correlation matrix of neutralizing activity against the wild-type-, Delta-, and Omicron-derived variants, anti-RBD antibody levels, and biomarker levels in vaccinated (n = 47) and unvaccinated patients (n = 20) at the acute phase of COVID-19 (within 5 days after symptom onset). Spearman correlation coefficients are plotted. Cells were colored according to the strength and trend of the correlations (shades of red = positive correlations, shades of blue = negative correlations). Anti-RBD antibody levels in the unvaccinated group were all negative (<0.4 U/mL). NT, neutralizing activity; WT, wild-type; RBD, receptor-binding domain; IFN, interferon; IL, interleukin; CXCL10, C-X-C motif chemokine ligand 10; VEGF, vascular endothelial growth factor; NLR, neutrophil-to-lymphocyte ratio; LD, lactate dehydrogenase; CRP, C-reactive protein; *P<0.05; **P<0.01; ****P<0.0001.

Figure 5

Relationship between neutralization activity against the Omicron-derived variant and IL-6, and the frequency of circulating follicular helper T cells in the CD4⁺ T cell population in vaccinated (n = 36) and unvaccinated patients (n = 17). (A) Representative flow cytometry plots of the gating strategy used to identify CXCR5⁺CD4⁺ cTfh cells. (B, C) Correlations between the cTfh cell population frequency and the neutralization activity against the Omicron-derived variant (red) or IL-6 levels (blue) in vaccinated (n = 37) (B) and unvaccinated patients (n = 17) (C). The Pearson correlation was calculated, and the P value and r value are shown. The general linear regression lines are shown. Each level was measured at admission (within 5 days after symptom onset) and each dot represents an individual value. cTfh, circulating follicular helper T; NT, neutralizing activity; IL, interleukin.