Immune System
T cell receptors (or TCR) on CD4+ T cells

are secreted out into the environment to bind antigens
recognize peptides not associated with MHC molecules
recognize peptides associated with MHC class II molecules
recognize peptides associated with MHC class I molecules

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Immune System
The role of the M cell is to

they use their cilia to propel mucus out of the small intestine
trap virus in mucus and prevent entry
induce apoptosis in virus-infected small intestinal epithelia cells
pass bacteria or virus to underlying macrophages for processing and presentation of antigen

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