*Article* **Longitudinal Development of Antibody Responses in COVID-19 Patients of Different Severity with ELISA, Peptide, and Glycan Arrays: An Immunological Case Series**

**Jasmin Heidepriem 1,†, Christine Dahlke 2,3,4,\*,†, Robin Kobbe 2, René Santer 5, Till Koch 2,3,4, Anahita Fathi 2,3,4, Bruna M. S. Seco 1, My L. Ly 2,3,4, Stefan Schmiedel 2, Dorothee Schwinge 6, Sonia Serna 7, Katrin Sellrie 1, Niels-Christian Reichardt 7,8, Peter H. Seeberger 1, Marylyn M. Addo 2,3,4,\*, Felix F. Loeffler 1,\* and on behalf of the ID-UKE COVID-19 Study Group ‡**


**Abstract:** The current COVID-19 pandemic is caused by the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). A better understanding of its immunogenicity can be important for the development of improved diagnostics, therapeutics, and vaccines. Here, we report the longitudinal analysis of three COVID-19 patients with moderate (#1) and mild disease (#2 and #3). Antibody serum responses were analyzed using spike glycoprotein enzyme linked immunosorbent assay (ELISA), full-proteome peptide, and glycan microarrays. ELISA immunoglobulin A, G, and M (IgA, IgG, and IgM) signals increased over time for individuals #1 and #2, whereas #3 only showed no clear positive IgG and IgM result. In contrast, peptide microarrays showed increasing IgA/G signal intensity and epitope spread only in the moderate patient #1 over time, whereas early but transient IgA and stable IgG responses were observed in the two mild cases #2 and #3. Glycan arrays showed an interaction of antibodies to fragments of high-mannose and core *N*-glycans, present on the viral shield. In contrast to protein ELISA, microarrays allow for a deeper understanding of IgA, IgG, and IgM antibody responses to specific epitopes of the whole proteome and glycans of SARS-CoV-2 in parallel. In the future, this may help to better understand and to monitor vaccination programs and monoclonal antibodies as therapeutics.

**Keywords:** SARS-CoV-2; COVID-19; full proteome; peptide microarrays; glycan microarrays

**Citation:** Heidepriem, J.; Dahlke, C.; Kobbe, R.; Santer, R.; Koch, T.; Fathi, A.; Seco, B.M.S.; Ly, M.L.; Schmiedel, S.; Schwinge, D.; et al. Longitudinal Development of Antibody Responses in COVID-19 Patients of Different Severity with ELISA, Peptide, and Glycan Arrays: An Immunological Case Series. *Pathogens* **2021**, *10*, 438. https://doi.org/10.3390/ pathogens10040438

Academic Editors: Philipp A. Ilinykh and Kai Huang

Received: 2 March 2021 Accepted: 1 April 2021 Published: 6 April 2021

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