The Role of Neutrophils in Rheumatoid Arthritis – Experiments In Vitro: A Change of Conception?

Essential cells of innate immunity, neutrophils are often considered to be a homogenous population of terminally differentiated cells (Chakravarti et al., 2009). These cells represent the body’s primary line of defence against invading pathogens such as bacteria, and constitute 40-60% of the white blood cell population. Neutrophils are short-lived polymorphonuclear phagocytes. They are known as first-responding inflammatory cells migrating towards the site of inflammation (Chakravarti et al., 2009; Edwards et al., 1997). In the circulation of healthy adults, neutrophils exist in a resting state, which ensures that their toxic intracellular contents are not accidentally released to damage host tissues. Neutrophils become activated by agents that include bacterial products and cytokines or chemokines, such as TNF-┙, IL-8 or IFN-┛. The primed neutrophils are then mobilized to the site of infection or inflammation and encounter activating signals to trigger bacterial killing. (Wright et al., 2010; Cascao et al., 2009) It must be noted, that the functions of resting blood neutrophils and primed neutrophils may be very different. Thus, many of the regulatory functions of macrophages are shared by primed (but not resting) neutrophils (Wright et al., 2010). For this reason, in vitro experiments using freshly isolated blood neutrophils often fail to recognize the full functional repertoire and capacity of neutrophils.