All authors reviewed the results and approved the final version of the manuscript. ACKNOWLEDGMENTS This study was supported from the Swedish State Support for Clinical Research (https://www.alfvastragotaland.se, ALFGBG\717531 [Magnus Gissln] and 679621 [Susannah Leach]), SciLifeLab/KAW national COVID\19 research system (https://www.scilifelab.se/covid-19#nationalprogram, V\2020\ 0250 [Magnus Gissln]) and Sweden’s Advancement Agency (Vinnova) project ID 2020\02205 (Ali M. the large family of coronaviruses (subfamily Orthocoronavirinae in the family of Coronaviridae of the order Nidovirales), seven are known to infect humans. Four endemic coronaviruses (eCoVs), the varieties HCoV\NL63 and HCoV\229E within the genus and the varieties HCoV\OC43 and HCoV\HKU1 within the genus where relevant) of N\specific antibodies against SARS\CoV\2 and the endemic coronaviruses. Samples collected within 10 days of sign onset in Covid\19 individuals with slight symptoms (n?=?21, blue) or severe/critical symptoms (n?=?22, red), and SARS\CoV\2\negative settings (n?=?27, green). (B) Serial samples collected during the 1st 30 days since sign onset in Covid\19 individuals with slight symptoms (n?=?5, blue) or severe/critical symptoms (n?=?18, red). Dotted collection in (A) shows assay cut\off for positivity for SARS\CoV\2 antibodies. ****p?0.0001, *p?0.05, ns: not significant There were no statistically significant correlations between the magnitudes of SARS\CoV\2 N\specific antibodies and any of the eCoV N\specific antibodies (data not demonstrated). This confirms that SARS\CoV\2 N\specific antibodies have no substantial mix\reactivity with eCoV epitopes in the C\terminal part of the N\protein used as antigen in the present study. Our getting on the lack of inverse correlation between eCoV N\specific antibodies and disease severity is definitely in line with, and stretches, a previous statement on the lack of mix\reactive neutralizing activity against SARS\CoV\2 in the pre\pandemic sera of individuals with prior PCR\confirmed eCoV illness. 12 As the samples in individuals with slight disease were collected mean 4 days earlier than in individuals with severe disease, the antibody levels in individuals with slight disease could be misleadingly low. To examine this, longitudinal samples retrieved from your same individuals during the first month of illness were analyzed. As expected, SARS\CoV\2 antibody levels increased significantly over time (r?=?0.4; p?=?0.003; Number?1B). In contrast, N\specific antibody levels to HCoV\NL63, HCoV\229E, and HCoV\OC43 did not increase over time, and HCoV\HKU1 antibodies actually showed a pattern toward decreasing over time (r?=??0.32; p?=?0.02). Therefore, the lack of difference between eCoV\specific antibodies in those individuals that are seriously ill and those that show only mild symptoms is definitely unlikely influenced from the 4\day time Efaproxiral difference in sampling timing. The eCoV N\specific antibody levels recognized in the samples probably reflect pre\existing serum antibodies, which do Efaproxiral not appear to have been boosted from the SARS\CoV\2 illness, supported by the fact that these serum antibody levels remain stable and even slightly decrease during the 1st month and don’t increase in parallel to the SARS\CoV\2 antibodies (Number?1B). Efaproxiral Notwithstanding, the possibility that memory space reactions to eCoV N\protein elicited by previous eCoV infections were very rapidly boosted by SARS\CoV\2 illness cannot be entirely ruled out. Additionally, it is conceivable that memory space B\cells specific for additional eCoV proteins, such as the S2 subunit,6, 7 with more mix\reactivity to SARS\CoV\2 counterparts, could be induced by SARS\CoV\2 illness. In conclusion, we report similar levels of eCoV N\specific antibodies early and during the 1st month after Efaproxiral the onset of symptoms in Covid\19 individuals with slight and severe symptoms. These results warrant further studies to investigate the MYH11 potential part of eCoV\specific antibodies in immunity to SARS\CoV\2 Efaproxiral illness. CONFLICT OF INTERESTS The authors declare that there is no discord of interests. AUTHOR CONTRIBUTIONS Study conception and design: Susannah Leach, Ali M. Harandi, Lars\Magnus Andersson, Lia vehicle der Hoek, and Magnus Gissln. Data collection: Susannah Leach, Lars\Magnus.