Evaluation of systemic and mucosal immune responses in mice administered with novel recombinant Salmonella vaccines for avian pathogenic Esherichia coli

Abstract

Avian pathogenic Escherichia coli (APEC) is a causative agent for a number of extra intestinal diseases and account for significant losses to the poultry industry. Since protective immunity against APEC is largely directed to virulence antigens, we have individually expressed four different viulence antigens, papA, papG, IutA, and CS31A, using an attenuated Salmonella Typhimurium and a plasmid pBB244. Following oral immunization of mice with combination of two or four of these strains, serum IgG and mucosal IgA responses were elicited against each antigen represented in the mixture. The antigen-specific mucosal IgA responses were significantly higher in the group of mice immunized with the heat-labile Escherichia coli enterotoxin B subunit (LTB) strain than those in the group of mice immunized without the LTB strain. While, there was no significant difference between these two groups in antigen-specific serum IgG responses. The results showed that LTB could act as mucosal immune adjuvant. To assess the nature of immunity, the distribution of antigen-specific IgG isotypes was analyzed. All groups promoted Th1-type immunity as determined by the IgG2a/IgG1 ratio. Thus, our findings provided evidence that immunization with a combination of several vaccine strains is one of the strategies of developing effective vaccines against APEC.

The B subunits of cholera and Escherichia coli heat-labile toxins enhance the immune responses in mice orally immunised with a recombinant live P-fimbrial vaccine for avian pathogenic E. coli

“…Plasmids pYA3493 and pYA3560 were described previously (Oh et al, 2011). All strains were grown at 37 °C in Luria-Bertani (LB) media (Difco, Sparks, MD, USA) with or without antibiotics.…”

“…Secreted antigen proteins from recombinant strains were obtained from cell-free culture supernatants by the TCA-precipitation process (Oh et al, 2011). Attenuated Salmonella containing the pYA3493 vector was used as control.…”

“…LTB and CTB proteins have been successfully expressed in different expression systems such as Mycobacterium bovis and Lactobacillus or Bacillus brevis (Slos et al, 1998;Hayward et al, 1999;Goto et al, 2000). Recently, live attenuated Salmonella bacteria were employed for delivery of antigens for mucosal vaccination (Branger et al, 2007, Oh et al, 2011. Salmonella bacteria as a carrier target the mucosal-associated lymphoid tissues in the gut and thereby improve the possibility of stimulating mucosal immunity, which may be important for providing protection against some infectious agents (Sirard et al, 1999).…”