Mononuclear phagocytes phagocytosis

Two major classes of WBCs are involved in removing invading microorganisms by a process of phagocytosis. These are polymorphonuclear leukocytes and mononuclear phagocytes, or monocytes. In tissues, monocytes differentiate into macrophages and, in the brain, into microglia... 

Clearance of endogenous and exogenous immunoglobulin takes place via a number of mechanisms. Among these are phagocytosis by mononuclear phagocytic cells (reticuloendothelial clearance), lymphatic clearance, and other tissue-specific and/or specialized mechanisms (discussed in more detail below). 

The main cells mediating phagocytosis are the mononuclear phagocytic cells and granulocyte cell populations of the latter neutrophils are particularly important. For such cells to function, they... 

Before consideration of the process of phagocytosis, an overview of the mononuclear phagocytic cell and granulocyte cell populations will be given. 

Tokuda, N. and Levy, R.B. (1996) 1,25-dihydroxyvitamin D3 stimulates phagocytosis but suppresses HLA-DR and CD13 antigen expression in human mononuclear phagocytes. Proceeding of the Society for Experimental Biology and Medicine, 211, 244—250. 

M,B. Lurie, Studies on the Mechanism of Immunity in Tuberculosis. The Mobilization of Mononuclear Phagocytes in Normal and Immunized Animals and Their Relative Capacities for Division and Phagocytosis, J. exp. Med. 69, 579-606 (1939). 

As stated previously, pSi particles are targets for internalization by cells of the mononuclear phagocyte system, and stealthing with PEG delays their uptake. For third-generation delivery systems, the first level of targeting for intravascularly administered particulates is the vascular endothehum. In vitro, vascular endothelial cells are able to internalize micron-sized pSi particles by phagocytosis and macropinocytosis (R.E. Serda et al, unpublished results). This is more compHcated in vivo, where serum opsonization coats the microparticles and alters their ability to adhere to the vascular wall. In this section we describe cellular uptake of pSi nanoparticles and microparticles, and examine the characteristics of pSi microparticles which alter this phenomenon. 

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