Specific amino acid (L-arginine) requirement for the microbiostatic activity of murine macrophages.

Abstract

The microbiostatic action of macrophages was studied in vitro employing peritoneal cytotoxic macrophages (CM) from mice acting against Cryptococcus neoformans cultured in Dulbecco's medium with 10% dialyzed fetal bovine serum. Fungistasis was measured using electronic particle counting after lysis of macrophages with detergent.Macrophage fungistasis failed in medium lacking only Larginine. Complete fungistasis was restored by L-arginine; restoration was concentration dependent, maximal at 200 MuM. Deletion of all other essential amino acids did not abrogate fungistasis provided that L-arginine was present. Of twenty guanido compounds, including D-arginine, only three (L-arginine, L-homoarginine, and L-arginine methylester) supported fungistasis. Known activators or mediators of macrophage cytotoxicity (endotoxin, interferon gamma, tumor necrosis factor) did not replace L-arginine for CM-mediated fungistasis. The guanido analogue NG-monomethyl-L-arginine was a potent competitive inhibitor of CM-mediated fungistasis giving 50% inhibition at an inhibitor/L-arginine ratio of 1:27. Although CM completely blocked fungal reproduction via an Larginine-dependent mechanism, the majority of the dormant fungi remained viable. Thus, this mechanism is viewed as a microbiostatic process similar or identical to the tumoristatic effect of macrophages. This suggests the production of a broad spectrum biostatic metabolite(s) upon consumption of L-arginine by cytotoxic macrophages.

Stimulation of Unprimed Macrophages with Immune Complexes Triggers a Low Output of Nitric Oxide by Calcium-dependent Neuronal Nitric-oxide Synthase

“…The role of NO production by macrophages during the phagocytosis of IC has mainly been associated with the cytotoxic activity of these cells for killing ingested or attached microbes (9,10). In fact, Fc␥R-mediated engulfment by macrophages has been consistently studied by first priming the macrophages with pro-inflammatory cytokines, which results in strong activation and secretion of high levels of NO.…”

“…Secretion of NO during Fc␥R engagement has conventionally been measured only when the macrophages are first primed with lipopolysaccharide (LPS) or cytokines such as IFN␥ and/or TNF␣ (6 -8). This results in high-output NO that can exert cytotoxic effects on a variety of pathogens, including bacteria, viruses, fungi, and parasites (9,10). However, the generation of low output NO by macrophages is emerging as an important event in the initiation or modulation of inflammatory responses.…”

Metabolic fate of L-arginine in relation to microbiostatic capability of murine macrophages.

“…Nitrite/nitrate synthesis occurs in vivo in mice during mycobacterial infection (7). Inhibition of the facultative intracellular pathogen, Cryptococcus neoformans, by macrophages in vitro depends upon the concentration of L-arginine available, in the extracellular environment, within the physiologic range (8). These findings implicate metabolism ofL-arginine by macrophages as a possible biochemical pathway for establishing and maintaining microbial dormancy.…”

IL-18 Contributes to Host Resistance Against Infection withCryptococcus neoformansin Mice with Defective IL-12 Synthesis Through Induction of IFN-γ Production by NK Cells

“…Cell-mediated immunity plays a major role in host defense (3)(4)(5)(6)(7), and Th1 cytokines, such as IFN-␥, which acts by inducing NO-dependent fungicidal activity of macrophages (8,9), are essential for this response (10). Many investigators have reported the essential role of IL-12, an important cytokine for differentiation of Th1 cells (11), in host resistance to a variety of infectious pathogens (12)(13)(14)(15)(16)(17).…”