Can Antigen Presenting Cells Aid in Diagnosis?
Organ-specific autoimmunity is often characterized by inflammatory infiltrates of mononuclear cells. In some cases, the infiltrate may be focal and hard to detect in a biopsy specimen. It is often easier to find such cells by staining the tissue with antibody to a T cell marker such as CD3 (a pan T cell molecule) or CD45RO (a marker of T memory and effector cells), but the infiltrate still may be missed in a particular section. A crucial aspect of T cell responses to antigen, including autoantigen, is that T cells actually respond to fragments of macromolecules (usually peptides) that are processed and then displayed while bound to major histocompatibility complex (MHC) molecules expressed on the surface of another cell. Cells of the mononuclear phagocyte lineage, especially myeloid dendritic cells and inflammatory macrophages, are adept at presenting antigens to T cells and are therefore sometimes called professional antigen-presenting cells (APCs). This is because professional APCs n
