Leishmania donovani amastigote component-induced colony-stimulating factor production by macrophages: modulation by morphine

The neuroimmunomodulatory effects of opiates during microbial infections are now well known; however, not much is known during leishmaniasis. Here, we report the effects of morphine on purified ~12-kDa component of Leishmania donovani amastigote antigen (LDAA-12)-induced colony-stimulating factor (CSF) production by mouse peritoneal macrophages (PMs) in vitro. Low concentrations (1 × 10-9 and 1 × 10-11 M) of morphine significantly (P < 0.05) augmented the production of CSFs, whereas high concentrations (1 × 10-3 and 1 × 10-5 M) inhibited CSF production. Morphine exerted a similar concentration-dependent biphasic effect on the LDAA-12-induced elaboration of granulocyte (G)-macrophage (M)-CSF (GM-CSF) and M-CSF by PMs in their conditioned medium, as quantified by using enzyme-linked immunosorbent assay. Furthermore, selective agonists of μ-(DAGO) and δ-(DPDPE) opioid receptors also, respectively, augmented and inhibited the production of CSFs. Pretreatment of PMs with naloxone (1 × 10-5 M) significantly (P < 0.05) blocked the augmenting effect of morphine. In contrast, at 1 × 10-5 M, naloxone lacked any effect on the inhibitory effect of morphine; however, its 100-fold higher concentration partially blocked it. This study, apparently for the first time, demonstrates that morphine, via surface opioid receptors, biphasically modulates the LDAA-12-induced CSF production by PMs, in vitro. These results thus show the implications of opiate abuse on the outcome of therapeutic interventions in areas where both visceral leishmaniasis and drug abuse are rampant.