Altered Cytokine Production in Mice Lacking P2X 7 Receptors

The P2X(7) receptor (P2X(7)R) is an ATP-gated ion channel expressed by monocytes and macrophages. To directly address the role of this receptor in interleukin (IL)-1 beta post-translational processing, we have generated a P2X(7)R-deficient mouse line. P2X(7)R(-/-) macrophages respond to lipopolysaccharide and produce levels of cyclooxygenase-2 and pro-IL-1 beta comparable with those generated by wild-type cells. In response to ATP, however, pro-IL-1 beta produced by the P2X(7)R(-/-) cells is not externalized or activated by caspase-1. Nigericin, an alternate secretion stimulus, promotes release of 17-kDa IL-1 beta from P2X(7)R(-/-) macrophages. In response to in vivo lipopolysaccharide injection, both wild-type and P2X(7)R(-/-) animals display increases in peritoneal lavage IL-6 levels but no detectable IL-1. Subsequent ATP injection to wild-type animals promotes an increase in IL-1, which in turn leads to additional IL-6 production; similar increases did not occur in ATP-treated, LPS-primed P2X(7)R(-/-) animals. Absence of the P2X(7)R thus leads to an inability of peritoneal macrophages to release IL-1 in response to ATP. As a result of the IL-1 deficiency, in vivo cytokine signaling cascades are impaired in P2X(7)R-deficient animals. Together these results demonstrate that P2X(7)R activation can provide a signal that leads to maturation and release of IL-1 beta and initiation of a cytokine cascade

The Effect of Adenosine on the Production of Inflammatory Mediators By Macrophages in Response to Candida Albicans

Mononuclear phagocytic cells (macrophages) are important cells of the immune system that are responsible for host defense to pathogenic organisms and infection. One pathogenic microorganism that can activate macrophages is the dimorphic fungus, Candida albicans. It is a major cause of candidiasis and is responsible for the development of serious, potentially fatal disease in predisposed patients. Upon activation, macrophages secrete inflammatory mediators, including the cytokines tumor necrosis factor alpha (TNF-α) and interleukin 1 (IL-1). Adenosine is an important physiological molecule that can modulate the function of macrophages by altering the amounts of cytokine produced. The effect of adenosine on the production of TNF-α and IL-1 by peritoneal macrophages was studied. Murine peritoneal macrophages stimulated with Candida albicans yeast cells secreted significant amounts of TNF-α and IL-1 over a 14 hr period. Various concentrations of adenosine (10-1000 μM) dose-dependently inhibited the production of TNF-α. Adenosine concentration of 1000 μM increased IL-1 production. The adenosine effect on IL-1 production was proven to be receptor mediated since the non-selective adenosine receptor antagonist (PACPX) was able to block IL-1 production. The results indicate that adenosine differentially affects the production of TNF-α and IL-1 in peritoneal macrophages in response to Candida albicans yeast