ABSTRACT
Monocytes are bone marrow derived cells that belong to the so-called innate immune system, along with central nervous system (CNS) microglia, dendritic cells, and polymorphonuclear leukocytes. Monocytes are phagocytic cells and secrete an array of inflammatory and cytotoxic mediators. Monocytes/ macrophages are not antigen specific, but when activated, macrophages express major histocompatibility (MHC) class II molecules that serve as antigen presenters to lymphocytes. Although the antigen binding to monocyteexpressed MHC structures is less discriminatory than the antigen-specific receptors of T and B lymphocytes, they represent a good example of the overlap that exists between the innate and adaptive immune system. Along with B and T lymphocytes, cells of the monocytes/macrophage lineage are hematogenous cells referred to as mononuclear cells (MNCs). Lymphocytes
andmonocytes exhibit a similar nuclearmorphology and nuclear-to-cytoplasmic ratio which is certainly relevant to the history of multiple sclerosis (MS), but also to the neuropathology of the disease. For years, lesions of MS have been recognized and described as areas of demyelination and perivascular accumulation of MNCs. It is only in the last two decades that the inflammatory infiltrate of MS lesions has been further defined in terms of the relative distribution of T and B lymphocytes, of monocytes and, of different subsets of these cells, based on recent advances in the molecular definition of immune cells subsets and advances in microscopy techniques.
