Inflammatory markers calprotectin, NETs, syndecan-1 and neopterin in COVID-19 convalescent blood donors

Abstract

Persisting inflammation has been discovered in lungs and other parenchymatous organs of some COVID-19 convalescents. Calprotectin, neutrophil extracellular traps (NETs), syndecan-1 and neopterin are general key inflammatory markers, and systemically enhanced levels of them may remain after the COVID-19 infection. These inflammatory markers were therefore measured in serum samples of 129 COVID-19 convalescent and 27 healthy blood donors or employees at Oslo Blood bank, Norway. Also antibodies against SARS-CoV-2 nucleocapsid antigen were measured, and timing of sampling and severity of infection noted. Whereas neopterin and NETs values remained low and those for syndecan-1 were not raised to statistically significant level, concentrations for calprotectin, as measured by a novel mixed monoclonal assay, were significantly increased in the convalescents. Antibodies against SARS-CoV-2 nucleocapsid antigen were elevated, but did not correlate with levels of inflammatory markers. Difference between the groups in only one biomarker makes evaluation of ongoing or residual inflammation in the convalescents difficult. If there is a low-grade inflammation, it would in that case involve neutrophils.

Keywords:

• Antibody response
• calprotectin
• convalescence
• COVID-19
• inflammation

Acknowledgement

The authors thank Department of Medical Biochemistry, Oslo University Hospital for the CRP measurements.

Ethical approval and patient consent statement

The study was approved by the independent ethics committee of Region South-East, Norway (REK number 124170), and all participants gave consent to research through Koronastsudien.no. The study was registered at www.clinicaltrials.gov (Identifier: NCT04320732).

Author contributions

GH interpreted the data and wrote the paper. MKF generated the novel Calprotectin Mimo, NETs and DNase ELISAs and MRM applied them on the blood samples. VPDS introduced the anti-SARS-CoV-2 assay into routine test repertoire at Microbiology Department and together with AL applied it on the samples. NTN did the neopterin test and interviewed participants, and SOK was responsible for the Syndecan-1 test. LSHNM collected the samples and was responsible for the biobanking and AVLS for regulatory issues regarding them. All authors read and commented on the paper and approved the final version of the manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

Data availability statement

The data supporting the findings of this study are available from the corresponding author upon request. The complete data are not publicly available due to ethical restrictions.

Additional information

Funding

The study was funded by Oslo University Hospital and University of Oslo, Norway.