Anti-Spike Protein Antibody Immunoreactivity Is Widely Expressed in Human Lymph Nodes with or without Pfizer-BioNTech or Moderna mRNA Vaccination in Non-Infected Individuals

The novel coronavirus SARS-coronavirus 2 (SARS-CoV-2) is the cause of the coronavirus disease 19 (COVID-19), the rapidly spreading pandemic. When SARS-CoV-2 enters the target cell, the spike (S) glycoprotein binds to a cellular receptor angiotensin converting enzyme 2 (ACE2). Effective vaccination has been achieved, utilizing the Spike (S) protein mRNA sequence. Objective: For a full understanding of the effects of Pfizer-BioNTech or Moderna mRNA vaccines, we evaluated the lymphoid responses. We have performed S protein western blots for proteins extracted from axillary lymph nodes, and S protein immunohistochemistry for the axillary lymph node tissues from human autopsies. Results: Our results showed that both vaccinated and control cases (non-vaccinated or negative for anti-S and anti-N antibodies) had positive S protein reactivity in both western blots and immunohistochemistry. This reactivity was present several months after vaccination. One anti-S protein antibody western blots showed a positive correlation with serum anti-S protein amounts. The positivity in non-vaccinated uninfected individuals indicates that either the antibodies against S protein are cross-reacting to other proteins present in human tissues, or due to insidious infections to SARS-CoV-2. Further evaluation is necessary for the reliability of anti-S protein antibodies in SARS-CoV-2 studies.