Giardia ADI was identified as the protein being responsible for a reduced NO response in in vitro interaction setups [9]. At least in vitro, NO acts cytostatic against G. intestinalis trophozoites

and inhibits encystation and excystation [10], the two differentiation processes essential for infection. It plays a role in muscle relaxation and thus in mechanical parasite elimination by peristalsis [11, 12]. Therefore reduction click here of the NO response of the host is in favor of Giardia growth. More recently, a NO-detoxifying enzyme (flavohemoglobin) was found in G. intestinalis, but its expression status upon host cell interaction has not been addressed yet [13, 14]. Therefore it needs to be investigated how exactly Selleck PD-332991 Giardia interferes with the NO response of human IECs. In mammalian cells, NO is formed either by NOS (eNOS, NOS3 in endothelial cells, nNOS, NOS1 in neuronal cells and iNOS, NOS2

in epithelial, endothelial and inflammatory cells) through conversion of arginine into citrulline and NO in an oxygen-dependent reaction, or through reduction of nitrite in various oxygen-independent ways [15]. NO has multiple roles in the human body, broadly taken together, as a cellular messenger and as an antimicrobial agent [15, 16]. NO reacts with reactive oxygen intermediates, forming antimicrobial substances such as nitrogen dioxide, peroxynitrite, S-nitrosothiols, dinitrogen trioxide and dinitrogen tetroxide that will cause damage in the cell wall, the DNA and the proteins of pathogens and also human cells [16]. However, effects of NO on Giardia trophozoites do not GABA Receptor seem to be exerted by peroxynitrite [17]. Many pathogens are known to interfere with the host’s arginine metabolism. Salmonella typhimurium,

Mycobacterium tuberculosis, Helicobacter pylori, Trypanosoma brucei and T. cruzi, Toxoplasma gondii and Schistosoma mansoni are known examples of pathogens that compete with host NOS for their common substrate arginine via up-regulation of host arginases [18, 19]. Some microorganisms are even known to consume arginine via their own arginases [18, 19]. Thereby pathogens can reduce host NO production and increase polyamine synthesis, which is in favor of pathogen growth and survival. However, within such studies it has neither been addressed what functions arginine-metabolizing enzymes apart from arginase or arginine transporters could play, nor has the direct consumption of arginine, or active detoxification of NO, by a pathogen been taken into account. As shown in previous microarray studies [20] a variety of chemokines are induced upon Giardia-host cell interaction that would be potent in attracting immune cells such as B and T cells, dendritic cells, macrophages, monocytes, mast cells and neutrophils to the intestinal mucosa.