key: cord-0871864-zp212xrs
authors: Focosi, Daniele; Moscato, Giovanna; Pistello, Mauro; Maggi, Fabrizio
title: Kinetics of anti‐SARS‐COV2 spike protein IgG and IgA antibodies at 4°C: Implications for convalescent plasma stability
date: 2021-04-25
journal: Transfus Med
DOI: 10.1111/tme.12776
sha: cf435f2e2c064b83bc0a785bcae85c0f6da5c045
doc_id: 871864
cord_uid: zp212xrs

nan

Dear Editor, Both diagnostic laboratory samples and convalescent plasma (CP) are usually preserved frozen at temperatures below À25 C for long-term storage. Nevertheless, investigating the stability of anti-SARS-CoV-2 antibodies at refrigerator temperature (+4 C) is of paramount importance in logistical settings where freezers are not available, or when usage cannot be accomplished within time limits after thawing imposed by law (usually 1-5 days, to preserve stability of labile clotting factors, as currently recommended by the European Commission) and plasma refreezing is not allowed by law.

We repeated anti-SARS-CoV-2 Spike (S) protein S1 subunit IgG and IgA testing with Euroimmun ELISA anti-SARS-CoV-2 kits (Euroimmun Medizinische Labordiagnostika AG, Lubeck, Germany) on 24 residual diagnostic serum samples stored at +4 C for variable amount of time after the initial determination, without any freeze/ thaw cycle. The study was approved by the internal review board (protocol 17437/2020). Statistical analyses were run using Spearman's Rho test on SPSS software v.23. The result plotted in Figure 1 , lower panel, shows that both IgG and IgA levels (expressed as ratio between sample and calibrator) linearly declined by up to 30% at day 95. There was no correlation between intensity of reduction and baseline antibody levels ( Figure 1, upper panel) , and, as per manufacturer's instructions for user, the intra-laboratory coefficient of variation for the assay run in the same lab at different timepoints is lower than 8% (data not shown). Preliminary reports by Stadlbauer et al. 1 showed stable IgG levels in 15 plasma samples for up to 42 days using an inhouse ELISA targeting the Spike protein: no details were disclosed regarding the kinetics of different immunoglobulin isotypes or the exact domain targeted by the assay. Our findings were instead achieved with a commercially available assay targeting the S1 subunit of the Spike protein: we extend the observation to 100 days, and for the first time report the kinetics of IgA isotype. 

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