Which cell type is capable of presenting extracellular antigens to CD4+ T cells via MHC class II?

Which cell type is capable of presenting extracellular antigens to CD4+ T cells via MHC class II?

• A. B cells
• B. Red blood cells
• C. Platelets
• D. Neutrophils

Answer: (A)

Presenting extracellular antigens to CD4+ T cells via MHC class II happens when professional antigen-presenting cells take up, process, and display peptides from outside the cell. B cells are capable of this because they can internalize antigens through their surface B cell receptors, chew them up in endosomal compartments, and load peptide fragments onto MHC class II molecules. When a CD4+ T cell recognizes that peptide–MHC II complex, the B cell can receive help from the T cell, activating processes that promote antibody production and class switching. B cells routinely express MHC class II and costimulatory molecules after activation, enabling effective communication with CD4+ T cells. Red blood cells lack nuclei and MHC class II expression, so they don’t present antigens to CD4+ T cells. Platelets are not professional APCs and don’t efficiently present peptides via MHC II. Neutrophils primarily engage in phagocytosis and microbial killing and are not the typical presenters of extracellular antigens to CD4+ T cells via MHC II.

Presenting extracellular antigens to CD4+ T cells via MHC class II happens when professional antigen-presenting cells take up, process, and display peptides from outside the cell. B cells are capable of this because they can internalize antigens through their surface B cell receptors, chew them up in endosomal compartments, and load peptide fragments onto MHC class II molecules. When a CD4+ T cell recognizes that peptide–MHC II complex, the B cell can receive help from the T cell, activating processes that promote antibody production and class switching. B cells routinely express MHC class II and costimulatory molecules after activation, enabling effective communication with CD4+ T cells.

Red blood cells lack nuclei and MHC class II expression, so they don’t present antigens to CD4+ T cells. Platelets are not professional APCs and don’t efficiently present peptides via MHC II. Neutrophils primarily engage in phagocytosis and microbial killing and are not the typical presenters of extracellular antigens to CD4+ T cells via MHC II.