Antigen-presenting cells (APCs) perform which of the following functions in adaptive immune responses?

Question

A. Display major histocompatibility complex (MHC)-associated peptides on their cell surfaces for surveillance by B lymphocytes
B. Initiate T cell responses by specifically recognizing and responding to foreign protein antigens
C. Display MHC-associated peptides on their cell surfaces for surveillance by T lymphocytes
D. Display polysaccharide antigens on their cell surfaces for surveillance by B lymphocytes
E. Secrete peptides derived from protein antigens for binding to T cell antigen receptors

Answer 1

ANS: C. Antigen-presenting cells (APCs) degrade proteins derived from either the extracellular environment or the cytoplasm. They form complexes of peptide fragments of these proteins with major histocompatability complex (MHC) molecules and display these complexes on their cell surfaces, where T cells can "see" them. Neither processing nor MHC association of protein or polysaccharide antigens by B cells is required for recognition. APCs do not distinguish between self and foreign proteins and will display peptides derived from a sampling of all cytoplasmic and extracellular proteins. APCs do not secrete peptide antigens, and T cell antigen receptors do not bind free peptides.