Phagocytes, professional

The neutrophils (also called polymorphonuclear leucocytes, PMNs), which are the professional phagocytes of the body. They constitute >70% of the total leucocyte population, remaining in the circulatory system for less than 48 hours before migrating into the tissues, in response to a suitable stimulus, where they phagocytose material. They possess receptors forFc and activated C3 which enhance their phagocytic ability (see later in chapter). 

The production of N-formylated proteins is a characteristic specific to bacteria and, therefore, an obvious target for the human immune system. It has been shown that professional phagocytes, the first line of defence against invading microorganisms, express receptors that recognise N-formylated peptides [12], and that activation of these receptors mediates migration of... 

K.H. Krause, Professional phagocytes predators and prey of microorganisms. Schweizerische Medizinische Wochenschrift 130, 97-100 (2000). 

Before we discuss how neutrophils (and other professional phagocytes) generate O2 and other oxygen metabolites during the respiratory burst, let us first consider why they produce such compounds. If these metabolites are produced in order to kill phagocytosed microorganisms, why and how are they toxic The answer comes from an examination of the chemistry of the oxygen molecule itself. 

Janssen K. P. and Schleicher M. (2001b) Dictyostelium discoideum a genetic model system for the study of professional phagocytes. Profilin, phosphoinositides and the Imp gene family in Dictyostelium. Biochim. Biophys. Acta. 1525, 228-233. 

For the purpose of completeness, the process of phagocytosis has been described briefly here. However, it should be remembered that phagocytosis is not generally relevant to the transport of drags across epithelial interfaces, as it is only carried out by the professional phagocytes of the MPS. 

It is well established that drugs of abuse are involved in a wdde range of immunomodulatory activities. Among the areas in immune system function in which these alterations have been observed is innate immunity. This arm of the immune system does not exhibit specificity in recognizing foreign pathogens. It encompasses NK cells and the professional phagocytic... 

However, these indirect effects of nitric oxide derived products are far more prevalent under pathological conditions such as inflammation, where the production of both NO and by the professional phagocytic cell NADPH oxidase enzyme, and induction of iNOS yields the potent cytotoxic species peroxynitrite. Whilst nitric oxide will react with metal centres (as discussed above) at a rate of 5x 10 M" s and the superoxide anion can be dismutated by SOD at a rate of 2.3x10 M s the combined reaction below (Eq. 9), proceeds at a rate faster than either of these individual reactions ... 

Phagocytosis Rapid removal by professional phagocytes and by neighboring cells... 

Ramarao, N., Gray-Owen, S.D., Backert, S., Meyer, T.F. (2000) Helicobacter pylori inhibits phagocytosis by professional phagocytes involving type IV secretion components. Mol. Microbiol. 37, 1389-1404. 

Phagocytosis occurs by profession phagocytes and by nonprofessional phagocytes. A professional phagocyte includes macrophages, monocytes, neutrophils and dendritic cell, while non-professional phagocytes are fibroblast, epithelial and endothelial cell [15, 16],... 

Uptake of particles by the epithelium is likely to be enhanced by airway surfactant and could account for the delayed clearance of fine and ultrafine particles from the airways noted in some studies (126,127). Forces from the free energy at interfaces and dividing lines might also contribute substantially to particle-cell interactions. These interactions are considered nonspecific, in contrast with the specific receptor-ligand interactions. Thus, nonspecific interactions could contribute to the uptake of particles by cells that are not professional phagocytes, such as epithelial cells. Epithelial cells of the airways take up particles such as silica and asbestos (128,129). 

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