Differential effector and secretory functions of microglial cell lines derived from BCG-resistant and -susceptible congenic mouse strains

Intracerebral Mycobacterium bovis bacilli Calmette-Guerin infection-induced immune responses in the CNS

To study whether cerebral mycobacterial infection induces granuloma and protective immunity similar to systemic infection, we intracerebrally infected mice with Mycobacterium bovis bacilli Calmette-Guerin. Granuloma and IFN-gamma(+)CD4(+) T cell responses are induced in the central nervous system (CNS) similar to periphery, but the presence of IFN-gammaIL-17 double-positive CD4(+) T cells is unique to the CNS. The major CNS source of TNF-alpha is microglia, with modest production by CD4(+) T cells and macrophage. Protective immunity is accompanied by accumulation of Foxp3(+)CD4(+) T cells and PD-L2(+) dendritic cells, suggesting that both inflammatory and anti-inflammatory responses develop in the CNS following mycobacterial infection.

A transmissible cytotoxic activity isolated from a patient with brain ischemia causes microglial cell activation and dysfunction

1. Microglial cell activation occurs during brain injury, ischemia, and in several neurologic disorders. Recently, we isolated a transmissible cytotoxic activity (TCA) from the cerebrospinal fluid of a patient with brain ischemia. Such a TCA, associated with one or more protein(s) that supposedly had undergone in vivo misfolding, causes apoptosis in vitro in different cell lines, including microglial cells. The TCA producing cells and the potential in vivo role of such cytotoxic activity remains to be elucidated. Here, we investigated the in vitro effects of TCA on microglial cell immune functions.2. The murine microglial cell line RR4 was exposed to TCA, and then its response was evaluated as: (a) phagocytosis and antifungal activity against Candida albicans; (b) secretory pattern; and (c) levels of p38 phosphorylation.3. Unlike mock-treated controls, microglial cells exposed to TCA showed an increase in phagocytic activity. Unexpectedly, their capability to kill the ingested fungi significantly diminished. Moreover, TCA-treated cells produced amounts of macrophage inflammatory protein 1-alpha, tumor necrosis factor-alpha, and nitric oxide significantly higher than mock-treated cells. Finally, phosphorylation of p38 mitogen-activated protein kinase (MAPK) was detected in TCA-treated but not in mock-treated controls as early as 30 min after treatment.4. Overall, these results indicate that TCA causes a rapid molecular response in microglial cells, by the time, leading to an intriguing effector and secretory dysfunction.

Cell culture isolation of a transmissible cytotoxicity from a human sample of cerebrospinal fluid

We investigated a transmissible cytotoxicity isolated in VERO cell cultures from a sample of cerebrospinal fluid (CSF) drawn from a woman with ischemic brain injury. Amorphous aggregates formed by subunities of approximately 11 nm of diameter were detected in ultracentrifugates from partially purified cytotoxic cell preparations in the absence of virion-like particles which might justify the trasmissibility of this cytotoxic activity. Results of chemico-physical studies provided indications on the presence in the CSF of two protease-resistant acidic glycoproteins of about 39 and 27 kDa, respectively. The conformational change of a proteinic molecule may associate with particular properties such as tendency to aggregation, resistance to proteolysis, cytotoxicity. Considering that these same properties are shared by proteins present in the CSF sample under study, a hypothesis to pursue is that the CSF inoculum we isolated contained misfolded proteins formed in vivo following the ischemic injury of brain tissue. As far as the in vitro transmissibility of the cytotoxic activity, this could take place following the reproduction of the alterations of those proteins, independently of the original cause(s) which have fostered their formation in vivo.

Differences in the amyloid-beta-induced inflammatory response in microglia from C57BL/6 and A/J strains of mice

The microglial inflammatory response to Abeta(1-42) stimulation with or without IFN-gamma priming was investigated in low and high responder strains of mice, A/J and C57BL/6, respectively. A/J microglia showed moderate morphological changes upon stimulation with IFN-gamma alone or with Abeta(1-42). Conversely, C57BL/6 microglia showed major changes in their cellular morphology, which were accompanied by a decrease in NO release and a marked increase in TNF-alpha production. These results indicate that the magnitude of the microglial inflammatory response to Abeta is strongly influenced by genetic factors. Individual differences in the regulation of the microglial response may be a key player in the rate of development of the neuropathology of AD.

Differential microbial clearance and immunoresponse of Balb/c (Nramp1 susceptible) and DBA2 (Nramp1 resistant) mice intracerebrally infected with Mycobacterium bovis BCG (BCG)

In mice, the gene encoding Nramp1 (natural resistance-associated protein 1) exists in two allelic forms, differing for a point mutation. According to Nramp1 genotype, extensive literature documents a clear-cut distinction of inbred strains in two non-overlapping groups that phenotypically express resistance (Nramp1r) and susceptibility (Nramp1s) to systemic infections. Here, we provide evidence that Nramp1r (DBA/2) and Nramp1s (Balb/c) mice differently handle intracerebral infection with Mycobacterium bovis BCG. Distinct trends of microbial clearance from the brain and also different patterns of local immune responses occur, thus arguing on the involvement of Nramp1 gene product on the accomplishment of cerebral anti-mycobacterial defenses.

Inactivation of peroxynitrite in multiple sclerosis patients after oral administration of inosine may suggest possible approaches to therapy of the disease

Peroxynitrite has been implicated in the pathogenesis of multiple sclerosis (MS) and its animal model experimental allergic encephalomyelitis (EAE). Previously, we have shown that administration of uric acid (UA), a peroxynitrite scavenger, is therapeutic in EAE We have also shown that MS patients have lower levels of serum uric acid than healthy individuals or those with other neurological diseases. The aim of this investigation was therefore to raise serum UA levels in MS patients. Oral administration of UA failed to increase low serum UA levels, evidently due to its degradation by gastrointestinal bacteria. However, serum UA could be raised and maintained at elevated levels for a year and more without reported side-effects by oral administration of its precursor inosine. Three of 11 patients given inosine showed some evidence of clinical improvement and there was no sign of disease progression in the remaining patients. Gadolinium-enhanced lesions, observed in two patients before receiving inosine, could not be detected after either 10 or IS months inosine treatment These data provide evidence that serum UA levels can be readily manipulated and that the benefit of higher levels to individuals with MS should be studied further in greater number of patients.

Uric acid levels in patients with multiple sclerosis: analysis in mono- and dizygotic twins

Presence of nitrotyrosine in cells surrounding plaques indicates that peroxynitrite may be the cause of brain lesions in multiple sclerosis. Low levels of uric acid, a natural scavenger of peroxynitrite, were demonstrated in blood of patients with multiple sclerosis in comparison with control individuals. These observations were now extended to 132 sets of twins with one sibling affected by multiple sclerosis. In blood of both mono- and dizygotic twins the uric acid levels were lower in the twin with the disease than in the healthy twin.