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
recognize peptides associated with MHC class II molecules
are secreted out into the environment to bind antigens

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Immune System
Polymorphonuclear leukocytes (or PMNs)

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

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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
Both (a) and (b)
By rearrangements of the DNA encoding the variable regions of the heavy and light chains

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