TRANSFORMING GROWTH FACTOR-BETA(1) PRIMES MACROPHAGES FOR ENHANCED EXPRESSION OF THE NITRIC-OXIDE SYNTHASE GENE FOR NITRIC OXIDE-DEPENDENT CYTOTOXICITY AGAINST ENTAMOEBA-HISTOLYTICA

Nitric oxide (NO) produced by activated macrophages is the major cytot oxic molecule for in vitro cytotoxicity against Entamoeba histolytica trophozoites. Transforming growth factor-beta(1) (TGF-beta(1)) is a po tent negative regulator of several macrophage functions, including NO production. In this study, we investigated the effect of TGF-beta(1) o n macrophage nitric oxide synthase (mac-NOS) mRNA expression and NO pr oduction for macrophage cytotoxicity against E. histolytica trophozoit es. TGF-beta(1) by itself was incapable of inducing mouse bone marrow- derived macrophage (BMM) amoebicidal activity and NO production (as me asured by nitrite). In contrast, TGF-beta(1) pretreatment (4 hr) prime d BMM for an enhanced amoebicidal activity of 15% and 23% in response to (interferon-gamma) IFN-gamma + tumour necrosis factor-alpha (TNF-al pha) or IFN-gamma + lipopolysaccharide LPS, concomitant with increased NO production of 85% and 27%, respectively. TGF-beta(1) pretreatment increased NO production in response to IFN-gamma + TNF-alpha/LPS stimu lation in a time- and dose-dependent manner. By Northern blot analysis , the increased NO production of TGF-beta(1)-pretreated BMM was preced ed by markedly enhanced expression of mac-NOS mRNA. The priming effect of TGF-beta(1) on NO production was critically dependent on both a TN F-alpha (greater than or equal to 100 U) and a LPS (greater than or eq ual to 100 ng) triggering dose in the presence of IFN-gamma. TGF-beta( 1) pretreatment enhanced TNF-alpha mRNA expression, but had no effect on TNF-alpha production in culture supernatants after 4 hr of stimulat ion with IFN-gamma + TNF-alpha/LPS; however, at a later time-point (16 -48 hr), even though the levels of TNF-alpha mRNA expression were unaf fected, TNF-alpha production was reduced. These data demonstrate that TGF-beta(1) priming for increased mac-NOS mRNA expression for NO-depen dent cytotoxicity against E. histolytica in response to IFN-gamma + TN F-alpha/LPS stimulation may be involved in the modulation of a TNF-alp ha triggering signal by TGF-beta(1).