Evaluation of Biochemical Differences and Immunostimulatory Properties of LPS and Lipid a Extracted From Brucella Strains

The intrinsic heterogeneity determination in Brucella Lipopolysaccharide (LPS) is important for explaining its chemical nature and biological behavior. This is significant for practical purposes, since LPS is the most relevant antigen during infection and vaccination. The purpose of the present study was to compare biochemical and immunological differences of LPS and lipid A in three strains of Brucella: B. melitensis (virulent strain), B. melitensis (vaccine strain, Rev1), and B. abortus (vaccine strain, S19). LPSs were extracted from Brucella strains using hot phenol-water method, and lipid A was obtained through mild acid hydrolysis. Glycan, phosphate, KDO, and protein concentration were evaluated in both LPS and lipid A samples. Immunological effects of Brucella LPS and lipid A were investigated measuring mitogenesis, IL-6, and Nitric Oxide (NO) production. LPS and lipid A of B. melitensis have more glycan, KDO, protein, and phosphate compared with B. abortus. Different species of Brucella LPS and lipid A induced NO production in a time- and dose-dependent manner via J774A.1 cells. One μg/ml LPS extracted from different strains of Brucella can induce maximum NO production. However, lipid A from S19 cannot induce NO and lipid A from B. melitensis induces NO production in higher doses of KDO than its LPS. Maximal production of IL-6 and higher mitogenic index in human lymphocytes was observed by Rev1 LPS. Regarding the diverse biochemical and immunostimulatory properties of LPS and lipid A, these strains of Brucella can be used potentially for different approaches, such as designing subunit brucellosis vaccines or effective adjuvants. For instance, LPS from B. abortus, as an effective and safe adjuvant due to its less toxicity, and Rev1 LPS, as subunit vaccines in developing anti-Brucella vaccines due to its high immunopotency, have been applied in several studies.