TLR4 and COVID-19: Another TLR4 agonist, inulin acetate (InAc), which is a plant-based polymer, has been reported to induce high IgG1, IgG2a, and sIgA titers against antigens in serum after intranasal immunization using antigen-loaded InAc nanoparticles (InAc-NPs); this approach resulted in a strong memory response indicative of both humoral and cellular immune activation, and may be useful in the development of a COVID-19 vaccine (Bakkari et al., 2021).