Immunostimulatory effects of isomalto/malto-polysaccharides via TLR2 and TLR4 in preventing doxycycline-induced cytokine loss

Isomalto/malto-polysaccharides (IMMPs) are α-glucans with prebiotic potential used as food ingredients. However, their ability to exert direct cellular effects remains unknown. IMMPs may enhance immunity by activating toll-like receptors (TLRs), key for defense against pathogens. Doxycycline is an antibiotic that requires an effective immune function but paradoxically has immune-attenuating effects by reducing TLR2 activity, potentially increasing antibiotic needs. We hypothesize that IMMPs are recognized by various cell surface TLRs, leading to the activation of the NF-κB signaling pathway. Furthermore, IMMPs' immune-stimulating effect could prevent the doxycycline-induced reduction of TLR2 activity in immune cells. IMMPs activated TLR2, increasing NF-κB signaling by 3.42- and 6.37-fold at 1 and 2 mg/mL, respectively. TLR4 activation increased 5.47-, 7.39-, and 8.34-fold at 0.5, 1, and 2 mg/mL. IMMPs enhanced IL-8, TNFα, and IL1-RA production in THP-1 monocytes. Additionally, preincubation of macrophages with IMMPs enhanced cytokine production and partially prevented doxycycline-induced cytokine reduction in response to TLR2 activation. Molecular docking analyses support IMMPs and doxycycline binding to these TLRs. These findings suggest that IMMPs stimulate immunity via TLR2 and TLR4, partially mitigating doxycycline's adverse effects. This provides a dietary strategy to enhance pathogen clearance, reduce antibiotic needs, and support immune health.