Long Term Disruption of Cytokine Signalling Networks are Evident Following SARS-CoV-2 InfectionSinead Ahearn-Ford1, Nonhlanhla Lunjani1, Brian McSharry1,2, John MacSharry1,2,3, Liam Fanning1,3, Gerard Murphy4, Cormac Everard4, Aoife Barry4, Aimee McGreal4, Sultan Mohamed al Lawati4, Susan Lapthorne4, Colin Sherlock4, Anna McKeogh4, Arthur Jackson4, Eamonn Faller4, Mary Horgan3,4, Corinna Sadlier4, Liam O’Mahony1,2,3*1APC Microbiome Ireland, University College Cork, Cork, Ireland2School of Microbiology, University College Cork, Cork, Ireland3Department of Medicine, University College Cork, Cork, Ireland4 Department of Infectious Diseases, Cork University Hospital, Cork, Ireland*Corresponding author – firstname.lastname@example.orgTo the Editor,The current pandemic caused by the SARS-CoV-2 virus has so far infected more than 130 million people worldwide, resulting in approximately 3 million deaths. While the current clinical and public health priorities are designed to limit severe acute and fatal episodes of the disease, and to quickly roll out vaccines to the general population, it has become apparent that there may also be significant detrimental long-term effects following SARS-CoV-2 infection that impact daily functioning and quality of life1. The mechanisms underpinning the post-acute sequelae of SARS-CoV-2 infection’s long-lasting symptoms can include direct effects of the infection (e.g. endothelial damage, lung fibrosis) or indirect effects associated with changes in the microbiome or abnormalities in inflammatory and immune signalling pathways stimulated by the infection2,3.In order to examine the potential long-term immune changes that occur following elimination of the primary infection, we examined the levels of 52 cytokines and growth factors (using MSD multiplex kits) in the serum of patients that attended follow-up post-COVID infection clinics at Cork University Hospital, Cork, Ireland (The Clinical Research Ethics Committee of the Cork Teaching Hospitals approved this study and all patients provided informed consent). All patients had been hospitalised for PCR-proven SARS-CoV-2 infection (median in-patient stay of 5.5 days, range 1 day to 24 days) during the first wave of the pandemic in Ireland (March-May 2020). 38 serum samples were obtained from 24 patients (median age 53.5 years, 11 female) at 3-9 months following hospital discharge. Clinical severity ranged from mild to critical during hospitalisation and the most common symptoms at follow-up clinics were fatigue and/or dyspnoea (supplementary Table S1). Sera obtained prior to the pandemic from 29 healthy volunteers (median age 43.2 years, 14 female) were analysed in parallel.Of the 52 analytes measured, 19 were significantly elevated in post-COVID patient sera compared to healthy controls (supplementary Table S2). These 19 mediators are illustrated as dot plots in Figure 1 and Figure 2. One group of mediators, c-reactive protein (CRP), serum amyloid A (SAA), Interleukin-1 receptor antagonist (IL-1RA), IL-6, IL-8, IL-15, IL-16, monocyte chemotactic protein (MCP)-1 and MCP-4, can be broadly categorised as being associated with ongoing inflammatory responses (Figure 1a)4. These mediators remained as elevated in samples taken 6-9 months following hospital discharge as those levels observed 3-6 months following discharge (p<0.05 versus controls, ANOVA). A second group of mediators, vascular endothelial growth factor (VEGF-A), soluble tyrosine-protein kinase receptor Tie-2 (Tie-2), soluble intercellular adhesion molecule (ICAM-1) and basic fibroblast growth factor (bFGF), can be generally associated with endothelial dysfunction, remodelling and angiogenesis (Figure 1b)5. The remaining elevated mediators are associated with patterns of lymphocyte polarisation. Elevated IL-4, macrophage-derived chemokine (MDC) and thymic stromal lymphopoietin (TSLP) sera levels indicate activation of TH2 responses (Figure 2a), while IL-17A, macrophage inflammatory protein (MIP)-3α and IL-12/23p40 indicate ongoing TH17 activity (Figure 2b). Other indicators of TH2-associated activities are just outside statistical significance (IL-5, p=0.06; supplementary Table S2). While TH1 responses are well described to be upregulated during acute infection6, the levels of these mediators (e.g. IFN-γ, IP-10) decrease following elimination of the virus and are at control levels in our cohort of post-COVID patients (supplementary Table S2).Our data suggests that there are long term immunological consequences following SARS-CoV-2 infection, at least in those that had acute symptoms severe enough to require hospitalisation. While the relatively low number of patients included in our study at this stage does not allow us to perform subgroup analysis, it is possible that these immune mediators may associate with clinically meaningful disease variables and ultimately may be of therapeutic value, if findings are replicated in future studies. Of particular interest is the elevation in TH2-associated mediators. Could this response be a component of the mucosal repair mechanisms that occur following viral damage, or does this indicate new TH2-associated pathological immune activity that might underpin an increased risk of developing allergy or asthma? Clearly the potential immune mechanisms underpinning the emerging post-COVID clinical entities will become increasingly more important to understand as the health care systems adapt to caring for large numbers of COVID-19 survivors during the coming months and years.