Mononuclear phagocytes and dendritic leukocytes in the skin

Abstract

P arasitic microorganisms have evolved to become dependent on other organisms for their successful life cycle. This is achieved through a variety of interactions with defined tissues, cells, and molecules of the parasite-carrier organisms (hosts/reservoirs, vectors). Whether transient or long-term, the parasitism is mediated by targeted molecular interactions between parasite ligands and host/vector counterligands synthesized through either a constitutive or an inducible program. In this review we shall describe the main interactions of protozoan parasites, namely Leishmania spp. within its mammalian host, focusing on the skin, the point of both entry/further dissemination and transmission of these parasites.re3 Within the skin, among the cells of hemopoietic origin that Leishmania spp. encounter and invade successfully are mononuclear phagocytes and dendritic leukocytes, the main properties of which will be delineated in the present chapter. Our emphasis will be on both the constitutive and inducible properties of the cells of these two related, although distinct, lineages in steady-state conditions and within the dynamic microenvironment of the Leishmania spp.-infected dermis, a compartment downstream of the epidermis and upstream of the draining lymph node. The lymph node is a specialized microenvironment where naive Leishmaniu reactive-T lymphocytes are expanded and programmed from which they will be released into the blood and enter the infected dermal microenvironment that they will modify through their ability to locally release cytokines.2,3