For the most part, you are correct, but the mRNA enters normal body cells not necessarily immune cells. To enter immune cells it has to be given in the form of a virus that targets immune cells. Once the mRNA is in the body cell, it uses the cell mechanism to proliferate and synthesis more mRNAs which will lead to the production of a protein.
Parts of this protein (it all depends on what the mRNA encodes for) will sit on the cells surface (either in the MHC 1 receptors or just on the surface) then the immune cells sees it on the surface of the cells and start their attack which will lead in most cases for the production of specific antibodies against this protein that originated from the mRNA.
That is how we develop antibodies against viruses. Since we are making the mRNA we develop it to encode for the protein that is present on the surface of the virus so the body will have immunity against the virus when it enters. More than one dose is required so the immune system can develop memory cells to remember the virus and attack quickly when it enters.
Market Data 
Markets 
AI
