Abstract
BackgroundThe aqueous extract of a Brazilian palm-tree fruit - the babassu - (BAE) exerts a clear immunostimulative activity in vivo. In the present work, the possibility that BAE can promote Th1 immune responses in mice of a Th2 immune response-prone strain - the BALB/c was investigated. BAE itself, and preparations consisting of Leishmania amazonensis promastigote extract (LE), adsorbed or not to Al(OH)3, and in the presence or not of BAE, were used as immunogens. LE and Al(OH)3 have been shown to preferentially elicit Th2 immune responses.ResultsThe addition of BAE to LE-containing immunogenic preparations, adsorbed or not to Al(OH)3, clearly promoted the in vitro production of interferon γ (IFN-γ), a major Th1-dependent cytokine, and not of interleukin (IL-)4 (a Th2-dependent cytokine), by LE-stimulated splenocytes of immunized BALB/c mice. It also promoted the in vivo formation of IgG2a anti-LE antibodies. However, immunization with LE by itself led to an increased production of IL-4 by LE-stimulated splenocytes, and this production, albeit not enhanced, was not reduced by the addition of BAE to the immunogen. On the other hand, the IL-4 production by LE-stimulated splenocytes was significantly lower in mice immunized with a preparation containing Al(OH)3-adsorbed LE and BAE than in mice immunized with the control preparation of Al(OH)3-adsorbed LE without BAE. Moreover, an increased production of IFN-γ, and not of IL-4, was observed in the culture supernatants of splenocytes, from BAE-immunized mice, which were in vitro stimulated with BAE or which received no specific in vitro stimulus. No differences in IL-10 (an immunoregulatory cytokine) levels in the supernatants of splenocytes from mice that were injected with BAE, in relation to splenocytes from control mice, were observed. The spontaneous ex vivo production of NO by splenocytes of mice that had been injected with BAE was significantly higher than the production of NO by splenocytes of control mice.ConclusionsBased on the results described above, BAE, or biologically active molecules purified from it, should be further investigated as a possible adjuvant, in association or not with aluminium compounds, for the preferential induction of Th1-dependent immune responses against different antigens in distinct murine strains and animal species.
Highlights
The aqueous extract of a Brazilian palm-tree fruit - the babassu - (BAE) exerts a clear immunostimulative activity in vivo
Anti-Leishmania amazonensis promastigote extract (LE) antibody levels The addition of babassu aqueous extract (BAE) to the antigenic preparations (both to LE or Al(OH)3 gel-adsorbed LE) led to significantly increased levels of serum anti-LE IgG2a antibodies in the immunized mice (Figure 1A, groups “LE + BAE” and “LE-Al(OH)3 + BAE”) in relation to the corresponding control mice that did not receive BAE (Figure 1A, groups “LE” and “LE-Al(OH)3“)
The co-administration of BAE led to a statistically significant increase in anti-LE IgG1 antibodies in the LE-immunized mice that have not received Al(OH)3 (Figure 1B, group “LE + BAE”) in relation to the mice that were immunized only with LE, without adjuvants (Figure 1B, group “LE”)
Summary
The aqueous extract of a Brazilian palm-tree fruit - the babassu - (BAE) exerts a clear immunostimulative activity in vivo. The oral administration of an aqueous extract of babassu mesocarp to mice increased the production of inflammatory mediators (such as hydrogen peroxide, nitric oxide and TNF-a) by peritoneal macrophages ex vivo and the influx of leukocytes to the peritoneal cavity [17]. These known immunostimulative effects of the babassu aqueous extract (BAE) have motivated the present investigation on its possible immunoadjuvant activity. The injection of BAE preferentially stimulated the Th1 component of the anti-LE and the anti-BAE immune responses in the immunized mice
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