Serum has antibodies to all antigens not present on its own cells. Note that because there are generally several clones that react with any given antigen, antibodies made in an animal are called polyclonal.
Class switching changes the constant region type.
Each stem cell produces an antibody with a different specificity, because it combines a different combination of V, D, and J exons for both light and heavy chains. B. T Cells T cells are lymphocytes that help activate the production of antibodies by B cells and kill foreign cells themselves. B cells then become plasma cells and secrete antibody. C. Cellular immunity Class I MHC, present on all cells, display pieces of antigen from the cells' normal proteins. If the cells are virus infected, they display pieces of viral proteins on their MHC Class I complexes and are also killed by TC cells.