title: Stimulus-response coupling in monocytes infected with Leishmania. Attenuation of calcium transients is related to defective agonist-induced accumulation of inositol phosphates.
abstract: Mononuclear phagocytes infected with Leishmania have been shown to have defective responses to extracellular stimuli. To investigate the potential relationship of these findings to alterations in calcium-dependent signaling pathways, the regulation of [Ca2+]i concentrations was examined in human peripheral blood monocytes infected with amastigotes of Leishmania donovani. Measurements of [Ca2+]i in fura-2-loaded monocytes were made at the single cell level by microfluorimetry. In normal monocytes, resting [Ca2+]i was 56 +/- 2 nM (mean +/- SEM). In contrast, in monocytes infected with Leishmania there was an approximately twofold increase in basal [Ca2+]i (122 +/- 5 nM, p less than 0.01 vs control). Treatment of cells with pertussis toxin before infection did not abrogate infection-induced increases in basal [Ca2+]i, suggesting that this effect was not mediated via the activation of a G protein coupled to phospholipase C. However, elevated resting [Ca2+]i did correlate with increased rates of 45Ca2+ uptake by infected monocytes. As expected, in response to treatment with 10(-7) M FMLP, control monocytes showed rapid net increases in [Ca2+]i of 303 +/- 19 nM. In contrast, net transients of [Ca2+]i in infected monocytes in response to FMLP were attenuated to only 137 +/- 9 nM (p less than 0.01 vs control). This result was not related to excess buffering of [Ca2+]i in infected cells as both control and infected monocytes showed equivalent transients of [Ca2+]i in response to the calcium ionophore A23187. Rather, inhibition of agonist-induced calcium release in infected cells appeared related to defective generation of second messenger because compared to control cells labeled with myo-[2-3H]inositol, little accumulation of inositol 1,4,5-trisphosphate was detected in infected monocytes. Attenuation of inositol phosphate accumulation and calcium release in response to chemotactic peptide correlated with decreased FMLP-induced superoxide and hydrogen peroxide production by infected monocytes. These results provide direct evidence for defective regulation of [Ca2+]i and calcium-dependent signaling in Leishmania-infected monocytes and provide a basis for understanding abnormalities in activation-related responses that involve signaling through Ca(2+)-regulated pathways.
authors.affiliation: Departments of Medicine, (Division of Infectious Diseases), University of British Columbia Faculty of Medicine, Vancouver, Canada.
authors.forename: M
authors.initials: M
authors.lastname: Olivier
authors.forename: K G
authors.initials: KG
authors.lastname: Baimbridge
authors.forename: N E
authors.initials: NE
authors.lastname: Reiner
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D006224:Cricetinae; D006861:Hydrogen Peroxide / Q000378:metabolism; D007295:Inositol Phosphates / Q000378:metabolism*; D007896:Leishmaniasis / Q000378:metabolism*; D008297:Male; D008647:Mesocricetus; D009000:Monocytes / Q000378:metabolism*; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D010084:Oxidation-Reduction; D015398:Signal Transduction
chemical_list: D007295:Inositol Phosphates; D009240:N-Formylmethionine Leucyl-Phenylalanine; D006861:Hydrogen Peroxide; D002118:Calcium