Canine histiocytic diseases: proliferation of dendritic cells is key

摘要

Macrophages and dendritic cells (DC) are collectively referred to as histiocytes. Histiocytes differentiate from CD34+ committed stem cell precursors into macrophages and a number of DC lineages, which include DC within epithelia also known as Langerhans cells (LC), interstitial DC in many organs, and interdigitating DC of T cell domains in peripheral lymphoid organs. Cytokines which influence DC development include GM-CSF, TNF-#alpha#, TGF#beta#, and IL-4. Macrophage development from CD34+ precursors is influenced by GM-CSF and M-CSF. Blood monocytes can differentiate into either macrophages under influence of M-CSF, or into interstitial DC under influence of GM-CSF and IL-4. Recently a new human DC lineage of myeloid origin was identified. TheseDC differentiate under the influence of GM-CSF and IL-3 and are the major source of non-activated resident DC in T cell domains of peripheral lymphoid organs. They are supplemented by migration of activated DC from skin and interstitial tissues, which arrive in lymph nodes as veiled cells in afferent lymph following contact with antigen. Macrophages and DC share many surface molecules that subserve common shared functions. Macrophages are more practiced in phagocytic/degradative functions, while DC areespecially adept in antigen presentation. Accordingly, DC express a greater array and/or concentration of antigen presenting and co-stimulatory molecules than do macrophages. For instance, DC express abundant CD1 and major histocompatibility complex (MHC) class II molecules, and also express co-stimulatory molecules such as B7-2 (CD86) in the resting state. Macrophages are capable of upregulating MHC class II and B7 molecules upon stimulation, but usually do not express abundant CD1 despite activation.