CD169 is a marker for highly pathogenic phagocytes in multiple sclerosis.

BACKGROUND: Phagocytes, such as macrophages and microglia, are key effector cells in the pathophysiology of multiple sclerosis (MS). It is widely accepted that they instigate and promote neuroinflammatory and neurodegenerative events in MS. An increasing amount of studies indicate that Siglec-1, also known CD169, is a marker for activated phagocytes in inflammatory disorders. OBJECTIVE: In this study, we set out to define how CD169+ phagocytes contribute to neuroinflammation in MS. METHODS: CD169-diphtheria toxin receptor (DTR) mice, which express human DTR under control of the CD169 promoter, were used to define the impact of CD169+ cells on neuroinflammation. Flow cytometry and immunohistochemistry were utilized to determine the expression and distribution of CD169. RESULTS: We show that CD169 is highly expressed by lesional and circulating phagocytes in MS and experimental autoimmune encephalomyelitis (EAE). Our data further indicate that CD169 represents a selective marker for early activated microglia in MS and EAE lesions. Depletion of CD169+ cells markedly reduced neuroinflammation and ameliorated disease symptoms in EAE-affected mice. CONCLUSION: Our findings indicate that CD169+ cells promote neuroinflammation. Furthermore, they suggest that CD169+ phagocytes play a key role in the pathophysiology of MS. Hence, targeting CD169+ phagocytes may hold therapeutic value for MS.

Ex vivo cultures of microglia from young and aged rodent brain reveal age-related changes in microglial function.

To understand how microglial cell function may change with aging, various protocols have been developed to isolate microglia from the young and aged central nervous system (CNS). Here we report modification of an existing protocol that is marked by less debris contamination and improved yields and demonstrate that microglial functions are varied and dependent on age. Specifically, we found that microglia from aged mice constitutively secrete greater amounts of interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) relative to microglia from younger mice and are less responsive to stimulation. Also, microglia from aged mice have reduced glutathione levels and internalize less amyloid beta peptide (Aß) while microglia from mice of all ages do not retain the amyloid beta peptide for a significant length of time. These studies offer further support for the idea that microglial cell function changes with aging. They suggest that microglial Aß phagocytosis results in Aß redistribution rather than biophysical degradation in vivo and thereby provide mechanistic insight to the lack of amyloid burden elimination by parenchymal microglia in aged adults and those suffering from Alzheimer's disease.

Detection of amyloid beta aggregates in the brain of BALB/c mice after Chlamydia pneumoniae infection.

Neuroinflammation, initiated by cerebral infection, is increasingly postulated as an aetiological factor in neurodegenerative diseases such as Alzheimer's disease (AD). We investigated whether Chlamydia pneumoniae (Cpn) infection results in extracellular aggregation of amyloid beta (Abeta) in BALB/c mice. At 1 week post intranasal infection (p.i.), Cpn DNA was detected predominantly in the olfactory bulbs by PCR, whereas brains at 1 and 3 months p.i. were Cpn negative. At 1 and 3 months p.i., extracellular Abeta immunoreactivity was detected in the brain of Cpn-infected mice but also in the brain of mock-infected mice and mice that were neither Cpn infected nor mock infected. However, these extracellular Abeta aggregates showed morphological differences compared to extracellular Abeta aggregates detected in the brain of transgenic APP751(SL)/PS1(M146L) mice. These data do not unequivocally support the hypothesis that Cpn infection induces the formation of AD-like Abeta plaques in the brain of BALB/c mice, as suggested before. However, future studies are required to resolve these differences and to investigate whether Cpn is indeed an etiological factor in AD pathogenesis.

Chlamydia pneumoniae infection of brain cells: an in vitro study.

Inspired by the suggested associations between neurological diseases and infections, we determined the susceptibility of brain cells to Chlamydia pneumoniae (Cpn). Murine astrocyte (C8D1A), neuronal (NB41A3) and microglial (BV-2) cell lines were inoculated with Cpn. Infection was established by immunofluorescence and real-time PCR at various time points. Productive infection was assessed by transferring medium of infected cells to a detection layer. Finally, apoptosis and necrosis post-infection was determined. Our data demonstrate that the neuronal cell line is highly sensitive to Cpn, produces viable progeny and is prone to die after infection by necrosis. Cpn tropism was similar in an astrocyte cell line, apart from the higher production of extracellular Cpn and less pronounced necrosis. In contrast, the microglial cell line is highly resistant to Cpn as the immunohistochemical signs almost completely disappeared after 24 h. Nevertheless, significant Cpn DNA amounts could be detected, suggesting Cpn persistence. Low viable progeny and hardly any necrotic microglial cells were observed. Further research is warranted to determine whether these cell types show the same sensitivity to Cpn in an in vivo setting.