Enhancement of serological immune responses to foot-and-mouth disease vaccine by a supplement made of extract of cochinchina momordica seeds

Abstract

Foot-and-mouth disease (FMD) is a highly contagious disease affecting cloven-hoofed animals. Vaccination against FMD is a routine practice in many countries where the disease is endemic. This study was designed first to investigate the extract of the seeds of Momordica cochinchinensis (Lour.) Spreng. (ECMS) for its adjuvant effect on vaccination of inactivated FMDV antigens in a guinea pig model and then to evaluate the supplement of ECMS in oil-emulsified FMD vaccines for its immunopotentiation in pigs. The results indicated that ECMS and oil emulsion act synergistically as adjuvants to promote the production of FMDV- and VP1-specific immunoglobulin G (IgG) and subclasses in guinea pigs. A supplement of ECMS in a commercial FMD vaccine significantly enhanced FMDV-specific indirect hemagglutination assay titers as well as VP1-specific IgG and subclasses in pigs. Therefore, ECMS could be an alternative approach to improving swine FMD vaccination when the vaccine is poor to induce an effective immune response.

FIG. 1.

FMDV-specific IgG, IgG1, and IgG2 in sera of guinea pigs (n = 6/group) immunized on days 1 and 21 by intramuscular injection of FMDV antigens (type O) in saline with or without ECMS (100 μg) or in oil emulsion with or without ECMS (100 μg). The animals without any injections were used as controls. Blood samples were collected before the first immunization and 2, 4, and 6 weeks after the boosting injection. FMDV-specific IgG and subclasses in the serum were measured by indirect double antibody sandwich ELISA as described in the text. The values are expressed as means ± SD. Bars with different letters at the same time point are statistically significantly different (P < 0.05). Bars with asterisks are statistically significantly different (P < 0.05) from those before immunization in the same group. OD, optical density.

FIG. 2.

FMD VP1-specific IgG, IgG1, and IgG2 in sera of guinea pigs (n = 6/group) immunized on days 1 and 21 by intramuscular injection of FMDV antigens (type O) in saline with (group 1) or without (group 4) ECMS (100 μg) or in oil emulsion with (group 2) or without (group 3) ECMS (100 μg). Group 5 was a control without any injection. FMD VP1-specific IgG and subclasses in the serum collected 4 weeks after the boosting injection were measured by indirect double antibody sandwich ELISA as described in the text. The values are expressed as means ± SD (n = 6). Bars with different letters are statistically significantly different (P < 0.05). OD, optical density.

FIG. 3.

IHA titers of sera from pigs (n = 6/group) immunized with a commercial FMDV (type O) vaccine (with oil as an adjuvant) alone (control) or mixed with ECMS (1, 2, or 4 mg). Blood samples were collected before and 3 weeks after immunization for measurement of IHA titers. Bars with different letters in the same time point are statistically significantly different (P < 0.01). Bars with asterisks are statistically significantly different (P < 0.05) from those before immunization in the same group.

FIG. 4.

IHA titers of sera from pigs (n = 12/group) immunized with a commercial FMDV (type O) vaccine (with oil as an adjuvant) alone (control) or in combination with ECMS (4 mg). Blood samples were collected before and 3 weeks after immunization for measurement of IHA titers. Bars with different letters in the same time point are statistically significantly different (P < 0.01). Bars with asterisks are statistically significantly different (P < 0.05) from those before immunization in the same group.

FIG. 5.

FMDV-specific IgG, IgG1, and IgG2 in sera of pigs (n = 6/group) immunized by intramuscular injection of FMDV antigens (type O) in saline with or without ECMS (100 μg) or in oil emulsion with or without ECMS (100 μg). Blood samples were collected before the first immunization and 3 and 6 weeks after the boosting injection. FMDV-specific IgG antibody in the serum was measured by indirect double antibody sandwich ELISA as described in the text. The values are expressed as means ± SD (n = 6). Bars with different letters at the same time point are statistically significantly different (P < 0.05). Bars with asterisks are statistically significantly different (P < 0.05) from those before immunization in the same group. OD, optical density.