Phagocyte/Phagocytosis

When a microorganism breaches the iititial barriers and enters the body tissues, the phagocytes form a formidable defence barrier. Phagocytosis is greatly enhanced by a family of proteins called complement. 

It has the ability to cross the placenta and therefore provides a major line of defence against infection for the newborn. This can be reinforced by transfer ofcolostral IgG across the gut mucosa of the neonate. It diffuses readily into the extravascular spaces where it can act in the neutralization of bacterial toxins and can bind to microorganisms enhancing the process of phagocytosis (opsonization). This is due to the presence on the phagocytic cell surface of a receptor for Fc. 

Phagocytosis The process of ingesting and destroying foreign material and debris by phagocytes. 

Compared with phagocytosis, pinocytosis appears to be a universal phenomenon in all cells, including phagocytes. Unlike phagocytosis, which is mediated by the serum opsonin, pinocytosis does not require any external stimulus. Pinocytosis is divided into two types fluid-phase pinocytosis and adsorptive pinocytosis (see Fig. 3B). Fluid-phase pinocytosis is a nonspecific, continuous process, and it is believed to be useful as a general process for transporting macromolecular constructs through epithelia, some endothelia, and into various blood cells. Adsorptive pinocytosis, in... 

Figure 8.9 Increased expression of IgG Fc receptors on phagocytes results in enhanced phagocytosis. These receptors will retain opsonized (i.e. antibody-coated) infectious agents at their surface by binding the Fc portion of the antibody. This facilitates subsequent phagocytosis...

Non-specific immunity Peritoneal macrophage count and phagocytic activity Phagocytosis... 

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