MyD88 expression by CNS-resident cells is pivotal for eliciting protective immunity in brain abscesses

MyD88 KO (knockout) mice are exquisitely sensitive to CNS (central nervous system) infection with Staphylococcus aureus, a common aetiological agent of brain abscess, exhibiting global defects in innate immunity and exacerbated tissue damage. However, since brain abscesses are typified by the involvement of both activated CNS-resident and infiltrating immune cells, in our previous studies it has been impossible to determine the relative contribution of MyD88-dependent signalling in the CNS compared with the peripheral immune cell compartments. In the present study we addressed this by examining the course of S. aureus infection in MyD88 bone marrow chimaera mice. Interestingly, chimaeras where MyD88 was present in the CNS, but not bone marrow-derived cells, mounted pro-inflammatory mediator expression profiles and neutrophil recruitment equivalent to or exceeding that detected in WT (wild-type) mice. These results implicate CNS MyD88 as essential in eliciting the initial wave of inflammation during the acute response to parenchymal infection. Microarray analysis of infected MyD88 KO compared with WT mice revealed a preponderance of differentially regulated genes involved in apoptotic pathways, suggesting that the extensive tissue damage characteristic of brain abscesses from MyD88 KO mice could result from dysregulated apoptosis. Collectively, the findings of the present study highlight a novel mechanism for CNS-resident cells in initiating a protective innate immune response in the infected brain and, in the absence of MyD88 in this compartment, immunity is compromised

Tissue-specific induction of ADAMTS2 in monocytes and macrophages by glucocorticoids.

The regulated expression of ADAMTS2 (a disintegrin and metalloproteinase with thrombospondin motifs), a secreted metalloproteinase involved in the processing of procollagen to collagen, was studied in peripheral blood mononuclear cells (PBMC). Stimulation with glucocorticoids (GC) resulted in a pronounced dose- and time-dependent increase of ADAMTS2 mRNA levels in PBMC. The increase of ADAMTS2 expression was specific for CD14++ monocytes (440-fold) and alveolar macrophages (200-fold), whereas CD3+ (T lymphocytes), phytohemagglutinin-activated CD3+ (T lymphocytes), and CD19+ (B lymphocytes) showed no significant changes in ADAMTS2 mRNA after GC treatment. Treatment of monocyte-derived macrophages (MDM) with GC also resulted in an increase of ADAMTS2 protein in the culture tissue media. Using the GC analog RU486, GC-mediated induction of ADAMTS2 mRNA was blocked, implicating that GC acts specifically via the GC-receptor. In agreement with findings in blood monocytes, cell lines of the monocytic lineage (MM6, THP-1) showed significant GC-induced significant increases in ADAMTS2 mRNA, while in epithelial cells (A549, Calu-3, Colo320, BT-20) and fibroblast (MRC-5, WI-38, and two NHDF-c cell types from adult cheek and upper arm), they showed no or little responsiveness to GC. As macrophages have important functions in immune defense and tissue homeostasis, these findings suggest that GC-mediated specific induction of ADAMTS2 in these cells may play a crucial role in the resolution of inflammation and wound repair