Oral administration of recombinant Lactococcus lactis expressing antigen VP8 rotavirus induces a specific immune response in mice.

BELKIS MARELLI; DIEGO DE MENDOZA; CHRISTIAN MAGNI

Rosario

Congreso; V Congreso Argentino de Microbiología General; 2008

Sociedad Argentina de Microbiología

Interest in the use of lactic acid bacteria (LAB) as delivery vehicles was focused on the development of mucosal vaccines given that a delivery system is needed to avoid degradation and promote uptake of the antigen in the gastrointestinal tract, and stimulate adaptive immune responses, rather than the tolerogenic immune responses that are seen with soluble antigens. The choice of LAB is based on a number of properties which render them particularly attractive as potential vaccine vehicles. They are considered as GRAS organisms (Generally Recognized As Safe) with a very long record of safe consumption. Rotavirus is the most cause of severe diarrhea in children younger than five years of age world-wide. The outer layer of the infective particle is made up of VP7 and is decorated with spikes of VP4. To be fully infectious, VP4 must be cleaved by the intestinal trypsin, with the formation of VP5 and VP8. The infection with rotaviruses primarily stimulates an immune response to VP8, therefore this is considered a good candidate for a subunit vaccine. In this context, the use of L. lactis for the expression of vp8 would be a valuable technique for vaccination against rotavirus.   As the protective response depends on the location of the antigen, we assessed the potential use of L. lactis strains displaying either cytoplasmic or secreted VP8 protein for immunization trials. For this purpose, we constructed two lactococcal strains, LL(pCYT:vp8) and LL(pSEC:vp8). The production and targeting capacities of such recombinant strains were analyzed by Western blot. Then, four groups of mice (7-9 eight-week-old female Balb/c) were immunized intragastrically, two of them with a bacterial suspension containing 1x109 colony-forming units (CFU) of LL(pCYT:vp8) and LL(pSEC:vp8). The remaining two groups received saline solution (PBS) or L. lactis (LL) carrying the empty vector. The specific serum IgG and intestinal IgA induction against VP8 was measured by ELISA. The IgA levels were higher in the group LL(pCYT:vp8) with respect to the group LL (OD; means ± ESM: 2.3 ± 0.10 vs. 1.9 ± 0.06; p = 0.03) and PBS group (2.3 ± 0.10 vs. 1.14 ± 0.05; p = 0.001), while no response was observed in the group LL(pSEC:vp8). On the other hand, we did not observe a significant increase in the induction of specific serum IgG in the immunized mice in any case (p ³ 0.05). In conclusion, our study allowed us to determine that the strain LL(pCYT:vp8) can be used as delivery vehicles to successfully express VP8 viral protein and to elicit an local immune response (IgA) against the antigen VP8. Therefore this strain will be useful to explore new strategies of vaccination against rotavirus.