The mRNA lipid nanoparticles are not Spike Protein.
(1) Injected mRNA vaccines are endocytosed by antigen-presenting cells.
(2) After escaping the endosome and entering the cytosol, mRNA is translated into protein by the ribosome. The translated antigenic protein can stimulate the immune system in several ways.
(3) Intracellular antigen is broken down into smaller fragments by the proteasome complex, and the fragments are displayed on the cell surface to cytotoxic T cells by major histocompatibility complex (MHC) class I proteins.
(4) Activated cytotoxic T cells kill infected cells by secreting cytolytic molecules, such as perforin and granzyme.
(5) Additionally, secreted antigens can be taken up by cells, degraded inside endosomes and presented on the cell surface to helper T cells by MHC class II proteins.
(6) Helper T cells facilitate the clearance of circulating pathogens by stimulating B cells to produce neutralizing antibodies, and by activating phagocytes, such as macrophages, through inflammatory cytokines. BCR, B cell receptor; ER, endoplasmic reticulum; TCR, T cell receptor.
Spike Proteins in this process are never set loose into the circulatory system. Instead, they are broken up or presented on the cell surface to helper T cells by MHC class II proteins.