A novel adjuvant, a mixture of alum and the general opioid antagonist naloxone, elicits both humoral and cellular immune responses for heat-killed Salmonella typhimurium vaccine

In the current study, we tested the efficacy of the mixture of naloxone, an opioid
receptor antagonist, and alum, as a new adjuvant, in the induction of humoral and
cellular immunity in response to heat-killed Salmonella typhimurium (HKST) as a
model vaccine. BALB/c mice were divided into five groups. Mice in the experimental
groups received either the HKST vaccine alone or in combination with the adjuvant
alum, naloxone or the alum–naloxone mixture. Mice in the negative control group
received phosphate-buffered saline. All mice were immunized two times on days 0
and 14. Two weeks after the last immunization, immune responses to S. typhimurium
were assessed. Our results indicated that the administration of the alum–naloxone
mixture as an adjuvant increased the ability of the HKST vaccine to enhance
lymphocyte proliferation, shifted the immune response towards a T-helper 1 (Th1)
pattern and increased S. typhimurium-specific immunoglobulin G (IgG), IgG2a, IgG1
and the ratio of IgG2a to IgG1. This resulted in improved protective immunity
against S. typhimurium. In conclusion, the administration of the alum–naloxone
mixture as an adjuvant, in combination with the HKST vaccine, can enhance both
humoral and cellular immunity and shift the immune responses to a Th1 pattern