AlOH and AlP Adjuvants Promote Stimulation and Phagocytosis in RAW 264.7: New Findings in Particle Size, Buffers, and Antigen Adsorption
Georon Ferreira de Sousa, Jéssica Pires Farias, Kalil Cristhian Figueiredo Toledo, Eduardo Gimenes Martins, Deren Zehra Kocabiyik, Alceu Totti Silveira Junior, Artur Luís Hennemann, Koiti Araki, Luís Carlos de Souza Ferreira, Cristiane Moutinho-MeloIntroduction:
Aluminum adjuvants are essential components of many vaccines, enhancing antigen delivery and stimulating immune cell activation. While their long history of use underscores their effectiveness, understanding the optimal conditions for antigen adsorption remains a challenge. This study aimed to investigate the adsorption of the SARS-CoV-2 RBD protein to aluminum hydroxide gel (AlOH) and amorphous aluminum hydroxyphosphate (AlP) adjuvants, focusing on their physicochemical properties and ability to promote in vitro immunological responses.
Methods:
Characterization of the protein, adjuvants, and their respective systems was conducted using X-ray diffraction, spectroscopic techniques, dynamic light scattering (DLS), and scanning electron microscopy (SEM). RAW 264.7 cells were used to assess the biological effects of adjuvants.
Results:
Both AlOH and AlP induced a notable bias towards M1 activation, suggesting a stronger effector response. AlOH significantly increased IL-4 and TNF-α production, particularly in the Ly6C+ subset at 6 and 12 hours. AlP stimulated the production of IFN-γ, IL-4, and TNF-α in Ly6C+ cells during the initial six hours
Discussion:
It was shown that optimizing agitation, adsorption time, buffer, and pH was crucial for enhancing adsorption efficiency. Moreover, sonication-induced reduction in aluminum particle size was essential for promoting phagocytosis in RAW 264.7 cells. In addition, AlOH seems to promote more cell stimulation than AlP concerning the number of cells and cytokines released.
Conclusion:
These findings highlighted the importance of optimizing antigen adsorption onto aluminum adjuvants, showed different tools to analyze that interaction mechanism, and provided interesting insights for in vitro experiments using macrophages.