Crystal type, chain length and polydispersity impact the resistant starch type 3 immunomodulatory capacity via Toll-like receptors

Food ingredients that can activate and improve immunological defense, against e.g., pathogens, have become a major field of research. Resistant starches (RSs) can resist enzymes in the upper gastrointestinal (GI) tract and induce health benefits. RS-3 physicochemical characteristics such as chain length (DP), A- or B-type crystal, and polydispersity index (PI) might be crucial for immunomodulation by activating human toll-like receptors (hTLRs). We hypothesize that crystal type, DP and PI, alone or in combination, impact the recognition of RS-3 preparations by hTLRs leading to different RS-3 immunomodulatory effects. We studied the activation of hTLR2, hTLR4, and hTLR5 by 0.5, 1 and 2 mg/mL of RS-3. We found strong activation of hTLR2-dependent NF-kB activation with PI <1.25, DP 18 as an A- or B-type crystal. At different doses, NF-kB activation was increased from 6.8 to 7.1 and 10-fold with A-type and 6.2 to 10.2 and 14.4-fold with B-type. This also resulted in higher cytokine production in monocytes. Molecular docking, using amylose-A and B, demonstrated that B-crystals bind hTLR2 promoting hTLR2-1 dimerization, supporting the stronger effects of B-type crystals. Immunomodulatory effects of RS-3 are predominantly hTLR2-dependent, and activation can be tailored by managing crystallinity, chain length, and PI.