Having recently finished teaching a semester of microbiology ending with my favorite topic, immunology, I thought I would provide some summaries of three different types of antigen presentation:

1. Presentation of antigen by macrophages (MHC II + Ag) to CD T Cells (TCR + CD4) resulting in the activation of CD4+ Helper T Cells

2. Presentation of antigen by B Cells (MHC II + Ag) to CD T Cells (TCR + CD4) resulting in the activation of CD4+ Helper T Cells – specifically capable of activating B Cells that have ‘seen’ and taken up antigens that bind to their unique BCRs.

3. Presentation of antigen by Epithelial Cells (MHC I + Ag) to CD T Cells (TCR + CD8) resulting in the activation of Cytotoxic T Lymphocytes (CTLs) that will kill cells presenting this antigen. All Cells bear MHC I, enabling them to present endogenous, intercellular antigens such as infecting virus particles.