Glial activation in the setting of central nervous system inflammation is a key feature of the multiple sclerosis (MS) pathology. Monitoring glial activation in subjects with MS, therefore, has the potential to be informative with respect to disease activity. The translocator protein 18 kDa (TSPO) is a promising biomarker of glial activation that can be imaged by positron emission tomography (PET). To characterize the in vivo TSPO expression in MS, we analyzed brain PET scans in subjects with MS and healthy volunteers in an observational study using [11C]PBR28, a newly developed translocator protein-specific radioligand. The [11C]PBR28 PET showed altered compartmental distribution of TSPO in the MS brain compared to healthy volunteers (p=0.019). Focal increases in [11C]PBR28 binding corresponded to areas of active inflammation as evidenced by significantly greater binding in regions of gadolinium contrast enhancement compared to contralateral normal-appearing white matter (p=0.0039). Furthermore, increase in [11C]PBR28 binding preceded the appearance of contrast enhancement on magnetic resonance imaging in some lesions, suggesting a role for early glial activation in MS lesion formation. Global [11C]PBR28 binding showed correlation with disease duration (p=0.041), but not with measures of clinical disability. These results further define TSPO as an informative marker of glial activation in MS.

Viruses have been implicated in the development of neurodegenerative diseases, such as Alzheimer's, Parkinson’s, and multiple sclerosis. Human herpesvirus-6 (HHV-6) is a neurotropic virus that has been associated with a wide variety of neurologic disorders, including encephalitis, mesial temporal lobe epilepsy, and multiple sclerosis. Currently, the route of HHV-6 entry into the CNS is unknown. Using autopsy specimens, we found that the frequency of HHV-6 DNA in the olfactory bulb/tract region was among the highest in the brain regions examined. Given this finding, we investigated whether HHV-6 may infect the CNS via the olfactory pathway. HHV-6 DNA was detected in a total of 52 of 126 (41.3%) nasal mucous samples, showing the nasal cavity is a reservoir for HHV-6. Furthermore, specialized olfactory-ensheathing glial cells located in the nasal cavity were demonstrated to support HHV-6 replication in vitro. Collectively, these results support HHV-6 utilization of the olfactory pathway as a route of entry into the CNS.

Adjuvant properties of bacterial cell wall components like MPLA (monophosphoryl lipid A) are well described and have gained FDA approval for use in vaccines such as Cervarix. MPLA is the product of chemically modified lipooligosaccharide (LOS), altered to diminish toxic proinflammatory effects while retaining adequate immunogenicity. Despite the virtually unlimited number of potential sources among bacterial strains, the number of useable compounds within this promising class of adjuvants are few. We have developed bacterial enzymatic combinatorial chemistry (BECC) as a method to generate rationally designed, functionally diverse lipid A. BECC removes endogenous or introduces exogenous lipid A-modifying enzymes to bacteria, effectively reprogramming the lipid A biosynthetic pathway. In this study, BECC is applied within an avirulent strain of Yersinia pestis to develop structurally distinct LOS molecules that elicit differential Toll-like receptor 4 (TLR4) activation. Using reporter cell lines that measure NF-κB activation, BECC-derived molecules were screened for the ability to induce a lower proinflammatory response than Escherichia coli LOS. Their structures exhibit varied, dose-dependent, TLR4-driven NF-κB activation with both human and mouse TLR4 complexes. Additional cytokine secretion screening identified molecules that induce levels of tumor necrosis factor alpha (TNF-α) and interleukin-8 (IL-8) comparable to the levels induced by phosphorylated hexa-acyl disaccharide (PHAD). The lead candidates demonstrated potent immunostimulation in mouse splenocytes, human primary blood mononuclear cells (PBMCs), and human monocyte-derived dendritic cells (DCs). This newly described system allows directed programming of lipid A synthesis and has the potential to generate a diverse array of TLR4 agonist candidates.

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