Particulate Cell Wall Materials of Lactobacillus acidophilus as Vaccine Adjuvant

SIMPLE SUMMARY: Different materials such as aluminum salts and bacterial peptidoglycan are considered immunogenic enhancers. Lactobacillus acidophilus (LA), a Gram-positive bacterium also known as a probiotic, is considered safe, acts as an immune enhancer when purified to form a pure peptidoglycan particle and is a possible candidate for a vaccine adjuvant. LA particles (LAPs) treated with high-pressure homogenization (HPH) with the addition of trehalose and emulsifiers had an average diameter of 179 nm. A five-fold dosage of LAPs treated with HPH and additives can induce a higher antibody titer response compared with commercial adjuvants in murine species. In comparison with ISA70, LAPs can stimulate an even antibody titer response but this decreased more quicky after a few weeks in chickens. Different formulation combinations of carbomer and LAPs induce a similar antibody response to commercial ISA70 with no acute toxicity, suggesting that LAPs are a potent vaccine adjuvant. ABSTRACT: We evaluated Lactobacillus acidophilus (LA) for adjuvant application in animal vaccines. LA particles (LAPs) are made by treating LA with purification processes and high-pressure homogenization (HPH). We found that LAPs treated with HPH with trehalose and emulsifiers had an average particle size of 179 nm, considerably smaller than LAPs without additives. First, we evaluated the adjuvanticity of LAPs using a murine model with ovalbumin antigens, revealing that LAPs, especially in a five-fold concentration, could induce a considerable antibody response compared with other current adjuvants. In poultry vaccination tests using inactivated Newcastle disease virus, LAPs alone could induce a similar antibody response compared to commercial water-in-oil (W/O) adjuvant ISA70, a commercial adjuvant, at weeks 4 and 6; however, they declined faster than ISA70 at weeks 8 and 10. LAPs added to conventional adjuvant materials, such as mineral oil-based O/W emulsions, showed similar adjuvanticity to ISA70. LA-H5-C, composed of carbomer, emulsifiers and trehalose showed no significant body weight change in acute toxicity compared to other adjuvants including ISA70, making formulated LAPs a potential candidate for use as a veterinary vaccine adjuvant.