Down-regulation of cell surface CXCR4 by HIV-1.

BACKGROUND: CXC chemokine receptor 4 (CXCR4), a member of the G-protein-coupled chemokine receptor family, can serve as a co-receptor along with CD4 for entry into the cell of T-cell tropic X4 human immunodeficiency virus type 1 (HIV-1) strains. Productive infection of T-lymphoblastoid cells by X4 HIV-1 markedly reduces cell-surface expression of CD4, but whether or not the co-receptor CXCR4 is down-regulated has not been conclusively determined. RESULTS: Infection of human T-lymphoblastoid cell line RH9 with HIV-1 resulted in down-regulation of cell surface CXCR4 expression. Down-regulation of surface CXCR4 correlated temporally with the increase in HIV-1 protein expression. CXCR4 was concentrated in intracellular compartments in H9 cells after HIV-1 infection. Immunofluorescence microscopy studies showed that CXCR4 and HIV-1 glycoproteins were co-localized in HIV infected cells. Inducible expression of HIV-1 envelope glycoproteins also resulted in down-regulation of CXCR4 from the cell surface. CONCLUSION: These results indicated that cell surface CXCR4 was reduced in HIV-1 infected cells, whereas expression of another membrane antigen, CD3, was unaffected. CXCR4 down-regulation may be due to intracellular sequestering of HIV glycoprotein/CXCR4 complexes.

Rapidly activated microglial cells in the preoptic area may play a role in the generation of hyperthermia following occlusion of the middle cerebral artery in the rat.

Postischemic hyperthermia occurs after the occlusion of the middle cerebral artery (MCAO) with an intraluminal filament in rats. The cause of hyperthermia is presumed to be damage to the preoptic area, which is one of the temperature-regulatory centers of the hypothalamus. In the present study, reactions of microglial cells and astrocytes in the preoptic area were examined during the first 6 h following transient MCAO. Microglial cells and astrocytes were visualized with immunohistochemistry using antibodies against the CR3 complement receptor and the glial fibrillary acidic protein, respectively. One hour after the occlusion, activated microglial cells were observed in both the medial and lateral preoptic areas ipsilaterally, and in the medial preoptic area contralateral to the infarct. Following reperfusion, the activation of microglial cells decreased in the medial preoptic area of both hemispheres, and in the lateral preoptic area there was a loss of immunoreactive microglial cells. Fragmentation of astrocytic processes was detected in the lateral preoptic area, while in the ipsilateral medial preoptic area a moderate swelling was observed. Immunohistochemistry with an antibody against interleukin-1beta (IL-1beta) revealed scattered immunoreactive cells in both the ipsilateral and the contralateral medial preoptic area 2 h after the MCAO. Our results show that microglial activation in the preoptic area coincides with postischemic hyperthermia. However, an exclusive role for IL-1beta in the generation of hyperthermia is unlikely, and other factors are probably also responsible for postischemic hyperthermia.

Filament size influences temperature changes and brain damage following middle cerebral artery occlusion in rats.

Postischemic spontaneous hyperthermia as a complication of occlusion of the middle cerebral artery with an intraluminal filament has been observed by some authors, but many other reports do not discuss this factor. The possible reasons why some of the authors have not seen severe hyperthermia in their experiments include differences in surgical technique, the strain of animals, the type of the anesthesia, and the occluder filament. The aim of this study was to examine the changes in the core temperature of rats using different types of filaments. The middle cerebral artery was occluded for 2 h with three different types of filaments. The changes in the temperature were continuously monitored during occlusion and for the next 4 h. Groups with uncontrolled hyperthermia and with controlled normal core temperature were used. In addition, the necrotic and penumbral areas were measured 4 and 48 h after the ischemia in both groups. Spontaneous postischemic hyperthermia was detected using all types of filaments. A close correlation was found between the size of the occluder filament and the time-course and degree of hyperthermia. Moreover, the size of the filament correlated well with the size of the infarct at both 4 and 48 h after the occlusion. We suggest that filament size is a major contributor to the degree of hyperthermia and the development of brain damage in the middle cerebral artery occlusion model. Our results call attention to the need to standardize the methods used to screen for therapeutic agents for stroke.