Effect of Leishmania donovani lipophosphoglycan on ornithine decarboxylaseactivity in macrophages

Lipophosphoglycan (LPG), a major surface molecule from Leishmania donovani, stimulated ornithine decarboxylase (ODC) activity in macrophages in a dose - and time-dependent manner. LPG stimulated the rapid increase in ODC activ ity within 30 min after exposure, suggesting that the interaction of LPG wi th its receptor stimulated a specific signal transduction pathway. However, LPG-induced ODC activity was a transient event because 3 hr after exposure to LPG, no stimulation of ODC activity was detectable. ODC activity appear ed to be coupled to the activation of protein kinase C (PKC) in macrophages , as activators of PKC caused a rapid increase in the ODC activity. Macroph ages pretreated with LPG for I hr became unresponsive to subsequent stimula tion by the PKC activators 1-oleoyl-2-acetyl-glycerol and the calcium ionop hore A23187. In contrast, the ability of macrophages to express ODC activit y in response to the cyclic AMP analogue dibutyryl cyclic AMP was not impai red by LPG.