Oral co-delivery of Brucella abortus Omp19 increases dmLT mucosal antibody responses and improves protection against heat-labile enterotoxin oral challenge

MARTINEZ, FRANCO LUIS; BRUNO LAURA; CORIA, LORENA; CASSATARO JULIANA

Congreso; LXIV Reunión Anual de la Sociedad Argentina de Inmunología (SAI); 2016

EnterotoxigenicE. coli (ETEC) is the most commoncause of bacterial diarrhea both among children in developing countries and intravelers to these regions. ETEC causes disease by colonizing the smallintestine and producing enterotoxins. Both naturally acquired infection andoral-mucosal vaccination against heat-labile toxin (LT) or colonization factorscan induce protective immunity. LT is being used as oral adjuvant/antigen (Ag)in mice. Since its toxicity limits its practical use in humans, a double mutantof LT (dmLT) which is less toxic and retains its adjuvant properties is underclinical trial. Wepropose to use a bacterial protease inhibitor (U-Omp19 from Brucella)as platform to deliver antigens in oral formulations against infectiousdiseases. This protein can protect Ags delivered in oral vaccines fromdigestion and it can also trigger and direct the type of mucosal and systemicimmune responses. Thus in this work our aim was to investigate theeffect of U-Omp19 co-delivery on dmLT immunogenicity and protective efficacy.To this end CD1 mice were orally immunized at days 0, 28 and 42 with i) salineii) dmLT or iii) dmLT+ U-Omp19. Three doses of dmLT were studied alone or plusU-Omp19. Fecal and serum anti-LT antibodies (Abs) were evaluated by ELISA.Results obtained indicated that U-Omp19 co-delivery increased (P<0.05) the mucosal anti-LT Abs (IgAand IgG in fecal extracts) while anti-LT Abs elicited at sera were not changed. One month after lastimmunization mice were challenged orally with LT and 3h later each intestineand carcass was weighted (patent mouse gut assay). We have shown that U-Omp19when co-delivered with dmLT induced significant protection (P<0.05) against oral challenge withLT, while dmLT alone did not. All together our results indicated that U-Omp19 can help to reduce the dose of dmLT and canincrease dmLT efficacy to neutralize LT in vivo. So, U-Omp19 would be agood candidate to be included in dmLT vaccine formulations against ETEC.