Covalent Coupling of Palmitate to Ovalbumin Inhibits and Blocks the Induction of Oral Tolerance^*

Abstract

Oral tolerance is a phenomenon that may occur in animals exposed to soluble antigens for the first time by the oral route. In the present study, we show that oral tolerance against ovalbumin (Ova) can be obtained after intragastric administration of the antigen in the presence of free residues of palmitate. On the other hand, oral tolerance induction is blocked when the residues of palmitate are covalently bound to the antigen (Ova-palmitate conjugates). We have also noticed that oral administration of Ova-palmitate conjugates can boost and/or prime experimental animals for Ova-specific cellular and humoral systemic immune responses. Oral treatment with the conjugates also induces the production of local secretory immunoglobulin A (IgA) as measured in intestinal washes. Furthermore, Ova-palmitate given orally can inhibit oral tolerance induction by naõÈ ve Ova.

Expression of costimulatory molecules in antigen-activated peritoneal macrophages treated with either ovalbumin or palmitoyl-ova conjugates

“…Cell culture was performed as previously described (Oliveira et al 2002). Splenocytes (5 × 10 6 cells/mL) were cultured in complete medium (RPMI 1640; Sigma) supplemented with 2 mM Lglutamine (Sigma), 1 mM sodium pyruvate (Sigma), 5 × 10 −5 M 2-mercaptoethanol (MerckSchuchardt, Müchen, Germany), 50 penicillin IU/mL, and 10% heat-inactivated fetal calf serum (FCS-Interlab, São Paulo, Brazil).…”

“…It has been previously shown that the coupling of palmitoyl residues to Ova abolished the induction of oral tolerance in B6D2F1 mice (Oliveira et al 1998;Oliveira et al 2002). To determine whether this coupling might influence the activation of APCs, cells from PerC were cultured with Ova or palmitoyl-Ova at two different concentrations and evaluated for the expression of activation markers.…”

“…In an earlier studies, the nature of a soluble protein antigen (ovalbumin; Ova) was changed by coupling it to palmitoyl residues, which showed that this procedure did not interfere with the induction of immune responses in the animals that were injected with one, or another form of the antigen (Oliveira et al 1998;Oliveira et al 2002). However, when both the forms of the antigen were orally administered to mice, opposite effects were obtained, induction of oral toleranc by the native protein and development of humoral immune response by the lipid-conjugated protein (Oliveira et al 1998).…”

Ethanol affects the absorption and tissue distribution of orally administered antigens in mice

“…For instance, ethanol can alter the morphology and physiology of the intestinal wall, promote serious damage to the gastric mucosa by destroying 10-50% of villi and enhance intestinal permeability (Andrade et al 2006;Beck et al 1996). A previous study had shown that palmitoyl-ovalbumin (palmitoyl-ova), not the naïve ova, was efficient in generating the humoral and cellular immunity (Oliveira et al 2002). Palmitoyl-ova also stimulated the production of IgA antibodies (Oliveira et al 2002).…”

“…A previous study had shown that palmitoyl-ovalbumin (palmitoyl-ova), not the naïve ova, was efficient in generating the humoral and cellular immunity (Oliveira et al 2002). Palmitoyl-ova also stimulated the production of IgA antibodies (Oliveira et al 2002). By contrast, the levels of IgA antibodies were lower in the intestinal fluid from ethanol-treated mice (Gusmão et al 2004); however, systemic immunization and oral tolerance against palmitoyl-ova and ova, respectively, were not affected by ethanol (Gusmão et al 2004).…”