In humans, interferon γ (IFN-γ) receptor deficiency leads to a predisposition to mycobacterial infections and impairs the formation of mature granulomas. Interleukin-12 (IL-12) receptor deficiency was found in otherwise healthy individuals with mycobacterial infections. Mature granulomas were seen, surrounded by T cells and centered with epithelioid and multinucleated giant cells, yet reduced IFN-γ concentrations were found to be secreted by activated natural killer and T cells. Thus, IL-12–dependent IFN-γ secretion in humans seems essential in the control of mycobacterial infections, despite the formation of mature granulomas due to IL-12–independent IFN-γ secretion.

We established microRNA profiles from active and inactive multiple sclerosis lesions. Using laser capture microdissection from multiple sclerosis lesions to pool single cells and in vitro cultures, we assigned differentially expressed microRNA to specific cell types. Astrocytes contained all 10 microRNA that were most strongly upregulated in active multiple sclerosis lesions, including microRNA-155, which is known to modulate immune responses in different ways but so far had not been assigned to central nervous system resident cells. MicroRNA-155 was expressed in human astrocytes in situ, and further induced with cytokines in human astrocytes in vitro. This was confirmed with astrocyte cultures from microRNA-155-|-lacZ mice. We matched microRNA upregulated in phagocytically active multiple sclerosis lesions with downregulated protein coding transcripts. This converged on CD47, which functions as a ‘don’t eat me’ signal inhibiting macrophage activity. Three microRNA upregulated in active multiple sclerosis lesions (microRNA-34a, microRNA-155 and microRNA-326) targeted the 3′-untranslated region of CD47 in reporter assays, with microRNA-155 even at two distinct sites. Our findings suggest that microRNA dysregulated in multiple sclerosis lesions reduce CD47 in brain resident cells, releasing macrophages from inhibitory control, thereby promoting phagocytosis of myelin. This mechanism may have broad implications for microRNA-regulated macrophage activation in inflammatory diseases.

Understanding the mechanisms of immune cell migration to multiple sclerosis lesions offers significant therapeutic potential. This study focused on the chemokines CXCL12 (SDF-1) and CXCL13 (BCA-1), both of which regulate B cell migration in lymphoid tissues. We report that immunohistologically CXCL12 was constitutively expressed in CNS parenchyma on blood vessel walls. In both active and chronic inactive multiple sclerosis lesions CXCL12 protein was elevated and detected on astrocytes and blood vessels. Quantitative PCR demonstrated that CXCL13 was produced in actively demyelinating multiple sclerosis lesions, but not in chronic inactive lesions or in the CNS of subjects who had no neurological disease. CXCL13 protein was localized in perivascular infiltrates and scattered infiltrating cells in lesion parenchyma. In the CSF of relapsing–remitting multiple sclerosis patients, both CXCL12 and CXCL13 were elevated. CXCL13, but not CXCL12, levels correlated strongly with intrathecal immunoglobulin production as well as the presence of B cells, plasma blasts and T cells. About 20% of CSF CD4⁺ cells and almost all B cells expressed the CXCL13 receptor CXCR5. In vitro, CXCL13 was produced by monocytes and at much higher levels by macrophages. CXCL13 mRNA and protein expression was induced by TNFα and IL-1β but inhibited by IL-4 and IFNγ. Together, CXCL12 and CXCL13 are elevated in active multiple sclerosis lesions and CXCL12 also in inactive lesions. The consequences of CXCL12 up-regulation could be manifold. CXCL12 localization on blood vessels indicates a possible role in leucocyte extravasation, and CXCL12 may contribute to plasma cell persistence since its receptor CXCR4 is retained during plasma cell differentiation. CXCL12 may contribute to axonal damage as it can become a neurotoxic mediator of cleavage by metalloproteases, which are present in multiple sclerosis lesions. The strong linkage of CXCL13 to immune cells and immunoglobulin levels in CSF suggests that this is one of the factors that attract and maintain B and T cells in inflamed CNS lesions. Therefore, both CXCL13 and CXCR5 may be promising therapeutic targets in multiple sclerosis.