Immune System
Polymorphonuclear leukocytes (or PMNs)

are a type of phagocyte that can engulf and kill bacteria
can be attracted to the site of an infection following activation of complement
are derived from bone marrow stem cells
All of these

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

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

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Immune System
The role of the M cell is to

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

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