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The ribosomes use the mRNA blueprint (note: this molecule is not a Spike Protein) to translate into spike proteins (antigens) which are then broken up into fragments or taken up by helper T cells by MHC class II proteins. The process is a closed system which creates antibodies and cytolytic molecules, such as perforin and granzyme.
“translate into spike proteins” which are circulated around the blood stream where the immune system can be triggered.