Conclusion
Overall, our findings indicate that iSARS-CoV-2 can induce properties associated with trained immunity in human monocytes. These results contribute to the knowledge required for improving vaccination strategies to prevent infectious diseases.
Methods
Monocytes were exposed to inactivated SARS-CoV-2 (iSARS-CoV-2) for 24 h, followed by a resting period in the medium only and a secondary stimulation on day 6 after which the cytokine/chemokine and transcriptomic profiles were determined.
Results
Compared to untrained cells, the iSARS-CoV-2-trained monocytes secreted significantly higher levels of IL-6, TNF-α, CXCL10, CXCL9, and CXCL11 upon restimulation. Transcriptome analysis of iSARS-CoV-2-trained monocytes revealed increased expression of several inflammatory genes. As epigenetic and metabolic modifications are hallmarks of trained immunity, we analyzed the expression of genes related to these processes. Findings indicate that indeed SARS-CoV-2-trained monocytes show changes in the expression of genes involved in metabolic pathways including the tricarboxylic acid cycle, amino acid metabolism, and the expression of several epigenetic regulator genes. Using epigenetic inhibitors that block histone methyl and acetyltransferases, we observed that the capacity of monocytes to be trained by iSARS-CoV-2 was abolished.