APCs, MHCs and lymphocytes
An antigen-presenting cell (APC), such as a macrophage, engulfs a foreign antigen, partially digests it in a lysosome, and then embeds it in an MHC class II molecule for presentation at the cell surface. Lymphocytes of the adaptive immune response must interact with antigen-embedded MHC class II molecules to mature into functional immune cells.
Source
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"Robert Bear and David Rintoul, Adaptive Immunity. December 11, 2013."
http://cnx.org/content/m47434/latest/
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