Acylated and deacylated quillaja saponin-21 adjuvants have opposite roles when utilized for immunization of C57BL/6 mice model with MOG35-55 peptide.

The majority of patients with multiple sclerosis (MS) suffer from central neuropathic pain (CNP). Using experimental autoimmune encephalomyelitis (EAE) model, only a few experiments were performed to assess pain behaviors in MS. To address this issue, complete Freund's adjuvant (CFA) was replaced with an acylated triterpene glycoside saponin adjuvant named quillaja saponin-21 (QS-21) to develop CNP in the EAE mouse model. The deacylated form of QS-21, named QT-0101, has been suggested to have an immunomodulatory effect. Thus, QT-0101 was used as a vaccine adjuvant to modulate the immune system against myelin oligodendrocyte glycoprotein (MOG35-55) antigen.

In this study, C57BL/6 mice, except for mice in the negative control (PBS) and MOG groups, were divided into three groups and immunized by MOG35-55 emulsified with CFA, QS-21, or QT-0101 adjuvants, respectively. Thermal hyperalgesia, as a CNP clinical manifestation, through the Hot Plate test and the clinical signs, was assessed for 60 days after immunization. On days 21 and 60, mice were sacrificed and the frequency of TCD4⁺, TCD8⁺, IL-17⁺, IL-4⁺, and CD25⁺/FoxP3⁺ cells population in the total splenocytes population was assessed by flow cytometry. Infiltration of Leukocytes into the brain and demyelination of white matter were also evaluated by histopathologic studies.

Our results revealed that unlike the MOG+QT-0101 group, the MOG+QS-21 and MOG+CFA groups represented clinical symptoms that mimic the mild relapsing-remitting and monophasic models, respectively. Thermal hyperalgesia, as a CNP clinical manifestation, developed in the bilateral hind paws in the MOG+CFA and MOG+QS-21 mice groups during the onset of neurologic deficits, but it is maintained until completion of the study only in MOG+QS-21 mice group. The frequency of TCD4⁺, TCD8⁺ and IL-17⁺ cells population in the MOG+QS-21 and MOG+CFA mice groups, as well as IL-4⁺ and CD25⁺/Foxp3⁺ cells population in the MOG+QT-0101 mice group, significantly increased in comparison with the PBS mice group. Infiltration of inflammatory cells increased significantly in the MOG+QS-21 and MOG+CFA mice groups compared with the PBS mice group. Demyelination of white matter was identified significantly only in the MOG+CFA mice group compared with the PBS mice group.

These results showed that QS-21 is a suitable adjuvant for the establishment of a mild relapsing-remitting EAE model for CNP development and open a new avenue to future pre-clinical and clinical research studies related to CNP treatment. Nevertheless, QT-0101 seems to have the potential to act as a vaccine adjuvant with immunomodulatory property against auto-antigens.