Immune System
Which is not an antigen-presenting cell (or APC)?

Dendritic cell
All of these
B cell
Polymorphonuclear leukocyte (or PMN)

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Immune System
Numerous antibodies can be prepared, against one antigen, each binds to unique epitopes. How is this antibody diversity generated?

Antibody proteins can physically change their shape to bind different epitopes
By the combination of different heavy and light chains that form the antigen binding site
By rearrangements of the DNA encoding the variable regions of the heavy and light chains
Both (a) and (b)

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

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

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Immune System
The role of the M cell is to

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
they use their cilia to propel mucus out of the small intestine

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