Contrasting Immune Responses in COVID-19: Insights from Healthcare Workers and Infected Patients on Plasmablast, pDC, and NK Cell Dynamics

Laura Martín-Pedraza^1,2,3*Eulalia Rodríguez-Martín^2,4Erick De La Torre Tarazona^1,2,3Elena Moreno^1,2,3Roberto Pariente Rodríguez^2,4Paulette Esperanza Walo-Delgado^2,4Javier García-Pérez^3,5JORGE DIAZ ALVAREZ^1,2,3Laura Luna^1,2,3Mario Rodriguez Dominguez^2,6,7Juan C Galan^2,6,7Claudia Geraldine Rita^2,4Ana del Amo-de Palacios^1,2,3Roser Navarro-Soler^1,2,3Maria Fons^1,2,3José Alcamí^3,5Santiago Moreno^1,2,3Luisa María Villar^2,4Sergio Serrano-Villar^1,2,3

• ¹Infectious Disease, Hospital Universitario Ramon y Cajal, Madrid, Spain
• ²Instituto Ramon y Cajal de Investigacion Sanitaria, Madrid, Spain
• ³Centro de Investigacion Biomedica en Red Enfermedades Infecciosas, Madrid, Spain
• ⁴Immunology, Hospital Universitario Ramon y Cajal, Madrid, Spain
• ⁵Instituto de Salud Carlos III, Madrid, Spain
• ⁶Microbiology, Hospital Universitario Ramon y Cajal, Madrid, Spain
• ⁷Centro de Investigacion Biomedica en Red de Epidemiologia y Salud Publica, Madrid, Spain

ABSTRACT Background: The COVID-19 pandemic, caused by SARS-CoV-2, has highlighted significant variability in disease severity, ranging from asymptomatic cases to severe acute respiratory distress syndrome. Objective: Understanding the immune responses that contribute to this variability, particularly among healthcare workers (HCWs) frequently exposed to the virus, is essential. Materials and Methods: This was a prospective single-center longitudinal cohort study. We included hospitalized COVID-19+ patients, classified as having mild or moderate-to-severe symptoms, and unvaccinated HCWs with low susceptibility. Peripheral blood mononuclear cells (PBMCs) were collected and analyzed using flow cytometry. We measured the frequencies of key immune subsets, including plasmablasts, plasmacytoid dendritic cells (pDCs), and Natural Killer (NK) cells. SARS-CoV-2 neutralizing antibodies (NAbs) were quantified using pseudotyped HIV particles. Results: COVID-19+ patients exhibited a significant increase in plasmablasts, a B-cell subset responsible for producing neutralizing antibodies, which correlated with disease severity (p=0.0082). Conversely, uninfected HCWs had low levels of plasmablasts but significantly higher levels of plasmacytoid dendritic cells (pDCs) (p<0.0001), which produce interferons upon activation by viral antigens. Additionally, HCWs had a higher percentage of CD56bright NK cells than the susceptible patients (p=0.02). Conclusion: Our findings suggest that immune dysregulation, characterized by increased plasmablasts and reduced pDC and NK cell responses, contributes to COVID-19 severity. Strong pDC and NK cell responses may confer protection against SARS-CoV-2. These insights into immune responses may inform strategies for therapeutic interventions and vaccine development.