Chemokine regulation of CNS T-cell infiltration in experimental autoimmune encephalomyelitis

The beta chemokines CCL4 and CCL5 enhance adhesion of specific CD4+ T cell subsets to human brain endothelial cells

Chemokines are key mediators of inflammation, acting as subset-specific chemoattractants and activators of leukocytes. In the present study we investigated the effects of chemokine concentration gradients on CD4+ T cell (TC4) adhesion to human brain microvessel endothelial cells (HBMECs) in vitro. CCL4 or CCL5 were placed in a double chamber chemotaxis system beneath confluent resting HBMEC monolayers or cultures co-incubated with TNF-alpha and IFN-gamma to mimic an inflammatory milieu. Chemokines readily diffused across activated HBMEC monolayers while binding to the sub-endothelial regions, establishing a chemotactic and haptotactic gradient. Naïve or resting TC4 adhered poorly to resting HBMECs compared to memory or recently activated TC4, but all subsets adhered more readily to cytokine-treated HBMECs. Chemokine gradients (10-100 ng/ml) of both CCL4 and CCL5 significantly enhanced the adhesion of memory and recently activated TC4 to cytokine-treated HBMECs, as much as doubling adhesion in a manner that correlated with chemokine receptor expression. Neither chemokine influenced adhesion to resting HBMEC monolayers nor the adhesion of resting or naïve TC4. These findings emphasize the role and importance of CNS-derived beta-chemokines in regulating the traffic of recently activated TC subsets (those previously localized to the CNS in vivo) across cytokine-activated cerebral endothelium in inflammatory diseases.

Targeting dipeptidyl peptidase IV (CD26) suppresses autoimmune encephalomyelitis and up-regulates TGF-beta 1 secretion in vivo

CD26 or dipeptidyl peptidase IV (DP IV) is expressed on various cell types, including T cells. Although T cells can receive activating signals via CD26, the physiological role of CD26/DP IV is largely unknown. We used the reversible DP IV inhibitor Lys[Z(NO(2))]-pyrrolidide (I40) to dissect the role of DP IV in experimental autoimmune encephalomyelitis (EAE) and to explore the therapeutic potential of DP IV inhibition for autoimmunity. I40 administration in vivo decreased and delayed clinical and neuropathological signs of adoptive transfer EAE. I40 blocked DP IV activity in vivo and increased the secretion of the immunosuppressive cytokine TGF-beta1 in spinal cord tissue and plasma during acute EAE. In vitro, while suppressing autoreactive T cell proliferation and TNF-alpha production, I40 consistently up-regulated TGF-beta1 secretion. A neutralizing anti-TGF-beta1 Ab blocked the inhibitory effect of I40 on T cell proliferation to myelin Ag. DP IV inhibition in vivo was not generally immunosuppressive, neither eliminating encephalitogenic T cells nor inhibiting T cell priming. These data suggest that DP IV inhibition represents a novel and specific therapeutic approach protecting from autoimmune disease by a mechanism that includes an active TGF-beta1-mediated antiinflammatory effect at the site of pathology.

Chemokines and their receptors in neurobiology: perspectives in physiology and homeostasis

Chemokines are a large family of small secreted proteins (8-14 kDa) associated with the trafficking of leukocytes in physiological immunosurveillance as well as inflammatory cell recruitment in different disease processes. A limited repertoire of chemokines and their specific cognate receptors are detectable in cells of the CNS such as microglia, astrocytes and neurons under physiological conditions. Coupled with distinct patterns of ligand and receptor expression in various pathologies including multiple sclerosis, trauma, neuro-AIDS, Alzheimer's disease, stroke, neuro- and glioblastomas, such phenomena have fueled the strong belief that chemokines must fulfill significant and potentially diverse functional roles in the CNS.