Induction of TLR2 activation depends on its association with the adapter protein MyD88. We have found that TLR2 and MyD88 levels are elevated in the hippocampus and cortex of patients with Alzheimer’s disease (AD) and in a 5XFAD mouse model of AD. Since there is no specific inhibitor of TLR2, to target induced TLR2 from a therapeutic angle, we engineered a peptide corresponding to the TLR2-interacting domain of MyD88 (TIDM) that binds to the BB loop of only TLR2, and not other TLRs. Interestingly, WT TIDM peptide inhibited microglial activation induced by fibrillar Aβ1-42 and lipoteichoic acid, but not 1-methyl-4-phenylpyridinium, dsRNA, bacterial lipopolysaccharide, flagellin, or CpG DNA. After intranasal administration, WT TIDM peptide reached the hippocampus, reduced hippocampal glial activation, lowered Aβ burden, attenuated neuronal apoptosis, and improved memory and learning in 5XFAD mice. However, WT TIDM peptide was not effective in 5XFAD mice lacking TLR2. In addition to its effects in 5XFAD mice, WT TIDM peptide also suppressed the disease process in mice with experimental allergic encephalomyelitis and collagen-induced arthritis. Therefore, selective targeting of the activated status of 1 component of the innate immune system by WT TIDM peptide may be beneficial in AD as well as other disorders in which TLR2/MyD88 signaling plays a role in disease pathogenesis.

Summary: Interleukin‐12 (IL‐12) p70 and IL‐23 are bioactive cytokines and their biological functions are becoming clear. Increased expression of IL‐7 in the central nervous system as well as in peripheral immune cells is associated with multiple sclerosis and experimental allergic encephalomyelitis. Here, we describe the induction of IL‐7 in primary mouse and human microglia, BV‐2 microglial cells, mouse peritoneal macrophages and astrocytes by IL‐12p70. Interestingly, IL‐12 strongly induced the expression of IL‐7 whereas IL‐23 and other p40 family members remained weak inducers of IL‐7 in these cell types. Consistently, IL‐12, but not IL‐23 and other p40 family members, induced IL‐7 promoter‐driven luciferase activity in microglial cells. Among various stimuli tested, IL‐12 emerged as the most potent stimulus followed by bacterial lipopolysaccharide and HIV‐1 gp120 in inducing the activation of IL‐7 promoter in microglial cells. Furthermore, increase in IL‐7 mRNA expression by over‐expression of IL‐12p35 subunit, but not p40 and IL‐23 p19 subunit, confirm that p35, but not p40 and p19, is responsible for the induction of IL‐7. Finally, by using primary microglia from IL‐12 receptor β1‐deficient (IL‐12Rβ1^−/−) and IL‐12Rβ2^−/− mice, we demonstrate that IL‐12 induces the expression of IL‐7 in microglia and macrophages via both IL‐12Rβ2 and IL‐12Rβ1. These studies delineate a novel biological function of IL‐12 that is absent in IL‐23 and other p40 family members.

Summary: Interleukin‐12 (IL‐12) p70 (p40:p35) is a bioactive cytokine and its biological functions are becoming clear. On the other hand, the IL‐12 p40 homodimer (p40₂) was considered an inactive or inhibitory molecule and its functions are poorly understood. It has been reported that increased expression of lymphotoxin‐α (Lt‐α) in the central nervous system as well as in peripheral immune cells is associated with multiple sclerosis and experimental allergic encephalomyelitis. Here we describe that p40₂ induces the expression of Lt‐α in primary mouse and human microglia, BV‐2 microglial cells, splenic macrophages, RAW 264.7 cells and splenic T cells. Interestingly, IL‐12 p70 was either unable to induce Lt‐α or was a very weak inducer of Lt‐α in these cell types. Consistently, p40₂, but not p70, induced Lt‐α promoter‐driven luciferase activity in microglial cells. Among various stimuli tested, p40₂ emerged as the most potent followed by IL‐16, lipopolyaccharide and double‐stranded RNA in inducing the activation of Lt‐α promoter in microglial cells. Furthermore, an increase in Lt‐α messenger RNA expression by overexpression of p40, but not p35, complementary DNA and induction of Lt‐α expression by p40₂ in microglia isolated from IL‐12p35^−/− mice confirm that p40, but not p35, is responsible for the induction of Lt‐α. Finally, by using primary microglia from IUL‐12 receptor β1 deficient (IL‐12Rβ1^−/−) and IL‐12Rβ2^−/− mice, we demonstrate that p40₂ induced the expression of Lt‐α in microglia and macrophages via IL‐12Rβ1, but not IL‐12Rβ2. These studies delineate a novel biological function of p40₂ that is absent in IL‐12.