Investigation of the Potential Immunomodulatory Effects of Some Medicinal Plants on the Immune Response of Layer Birds Vaccinated with a Live Salmonella gallinarum Vaccine

Plant-derived immunomodulators modulate adaptive immune responses to vaccines. The present study aims to investigate the acquired immune responses elicited by live attenuated Salmonella gallinarum vaccine complemented by some herbal extracts. Sixty chicks (one day old) were divided into six groups; Unvaccinated (NEG), Vernonia amygdalina (VA), Garcinia kola (GK), Curcuma longa (CL), Zingiber officinale (ZO), and polyherbal (PH) groups. The NEG group received distilled water, while the other groups were administered live attenuated Salmonella gallinarum vaccine intramuscularly (0.2 mL/bird) at 5 and 9 weeks. Aqueous extracts of the plants were administered singly, and in combination (2 mL/bird orally) at 7 and 11 weeks. At 8, and 12 weeks, circulating immunoglobulin G (IgG) antibody titres were evaluated using haemagglutination (HT) test and enzyme linked immunosorbent assay (ELISA). Cell-mediated response was evaluated using the delayed-type hypersensitivity response (DTHR) test.After primary immunization, IgG titres were significantly higher in the vaccinated groups (0.515 - 0.716) compared to the unvaccinated (NEG) group (0.364). After secondary immunization, there was a boost in the IgG titres, with the PH group exhibiting the highest IgG titre (0.768). The haemagglutination test showed the highest agglutination in the VA group (100%), followed by GK (80%), ZO/PH (60%), and CL (40%). Cell-mediated immunity after 24 h showed an insignificant increase in paw size of the vaccinated chicks, with the CL group showing the highest increase in paw size (3.2%). The results showed that the herbal extracts had immunomodulatory effects with some extracts enhancing the acquired immune responses while others suppressed it.