The emergence of SARS-CoV-2 and its global spread since late 2019 still has many gates that need to be open. However, continuous scientific research and experimentation have always provided researchers with something that become the basis of another deeper research for combating COVID- 19. One such is, the marked T cell reactivity, observed in the geographically diverse cohort study, against the peptides corresponding to SARS-CoV-2 sequences in the SARS-CoV-2 unexposed individuals (Bert et al., 2020; Meckiff et al., 2020).
This reactivity is predominantly mediated by CD4+ T cells, as observed in the in-vitro stimulation of PBMCs with pools of 15-primer peptides for the duration of 2-weeks (Mateus et al., 2020).To observe this cross-reactivity through in-vitro studies, peptides pools encompassing peptides homologous to HCoVs derived CD4-R30 epitopes and SARS-CoV-2 CD4-S31 epitopes were synthesized and analyzed by activation-induced marker assay to detect virus-specific T cells in unexposed donors as well as COVID-19 patients. It was observed that unexposed subjects showed significant frequencies of CD4+ T cells against CD4-R30 and CD4-S31 SARS-CoV-2 epitope pools.
Furthermore, T cell lines, generated from the CD4-R30 and CD4-S31 pools from the unexposed subjects, also showed that the memory CD4+ T cells which recognize common cold coronavirus can also exhibit substantial cross-reactivity to the homologous epitope in SARS-CoV-2. This might explain why some individuals have milder symptoms of COVID-19.
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Ref: Mateus, J., et al. (2020) Selective and cross-reactive SARS-CoV-2 T cell epitopes in unexposed humans. Science. doi. org/10.1126/science.abd3871