* Red blood cells (erythrocytes): Their primary function is oxygen transport, and they lack the necessary machinery for antigen presentation.
* Nerve cells (neurons): Their role is in transmitting information throughout the body, not in immune response.
* Muscle cells: They specialize in contraction and movement, and don't participate in antigen presentation.
* Epithelial cells: These cells form linings and coverings of the body, and while some can act as APCs in certain contexts, their primary role is protection.
* Gametes (sperm and egg): Their function is in reproduction, not immune response.
* Most cells within the central nervous system (CNS): The CNS has its own unique immune system, and its cells are generally shielded from the rest of the body's immune response.
Important Note: The list above is not exhaustive. There are many cell types in the body that are not APCs.
Key characteristics of APCs:
* Expression of MHC II molecules: These molecules present antigen fragments to CD4+ T cells, initiating an immune response.
* Ability to internalize and process antigens: APCs can engulf and break down antigens to present them on their surface.
* Ability to migrate to lymph nodes: This allows APCs to interact with T cells and initiate adaptive immune responses.
The most common APCs include:
* Dendritic cells: Highly efficient at capturing and presenting antigens to T cells, initiating adaptive immune responses.
* Macrophages: Engulf pathogens and present antigens to T cells, playing a key role in both innate and adaptive immunity.
* B cells: Present antigens to T cells during the process of antibody production.
