Purinergic mechanism in the immune system: A signal of danger for dendritic cells

There is increasing appreciation that injured or stressed cells release molecules endowed with the ability to modulate dendritic cell maturation. The role of these molecules is thought to be that of alerting the body of an impending danger, and initiate and shape the subsequent immune response. Nucleotides are perfectly suited for this task as they are easily released upon damage of the cell membrane, rapidly diffuse in the extracellular environment and ligate specific plasma membrane receptors expressed by dendritic cells and other mononuclear phagocytes. A better knowledge of the modulation of dendritic cell responses by extracellular nucleotides may provide novel routes to enhance the immune response and increase the efficacy of vaccination

Identification of a 120 kD ligand for human CD38 predominantly expressed by endothelial cells

Human CD38, a pleiotropic molecule with ADP-ribosyl cyclase activity, regulates activation and growth of several cell types. Its in vivo function is incompletely determined, mainly due to the lack of evidence concerning the existence of a single or multiple ligands. We recently observed that CD38 rules a selectin-type adhesion between lymphoid cells and HUVECs. A panel of murine mAbs raised against HUVEC included one (Moon-1) constantly blocking the CD38-mediated adhesion of several cell lines to HUVEC. Tissue distribution studies and an extended immunohistochemical analysis on the majority of normal human tissues revealed that the Moon-1 molecule displays a unique pattern of expression, being present at high levels on resting and activated vascular endothelium, on the majority of monocytes, platelets, NK cells, and to a lesser extent on T, B, and myeloid cells. The Moon-1 structure of an apparent molecular mass of 120 kDa proved to be a ligand for human CD38, as inferred by the direct binding observed when using a chimeric mouse CD8 alpha-human CD38 (mCD8 alpha-hCD38) molecule as a probe in Western blot experiments. Furthermore, Ab-induced modulation experiments highlighted an association between the Moon-1 molecule and human CD38 on the surface of cell lines coexpressing the two structures, which also share a common regulation system of surface expression. Finally, direct ligation of Moon-1 on T cell lines caused a relevant increase in the cytoplasmic concentration of calcium ([Ca2+]i)

Expression of low-density lipoprotein receptors in peripheral blood and tonsil B lymphocytes

B lymphocytes, purified from peripheral leucocytes from young normolipaemic humans, expressed and internalized low-density lipoprotein receptors (LDLR). The expression was assessed by a monoclonal anti-LDLR. The internalization of LDL was assessed by LDL labelled with 125I (125I-LDL) and 1,1′-dioctadecyl-3,3,3′,3′ tetramethyl-indocarboxycyanine perchlorate (LDL-DiI). The expression of LDLR, assessed by anti-LDLR, was: 38 ± 8% (n = 5) for fresh purified cells, 60 ± 10% (n = 12) for non-stimulated cells, 79 ± 5% (n = 10) for IL-2 (100 U/ml)-stimulated cells and 95 ± 5% (n = 8) for pokeweed mitogen (PWM) (1:200 dilution)-stimulated cells. The optimal concentrations of agonist were 100 U/ml of IL-2, and 1:200 dilution of PWM. IL-2 and PWM increased the internalization of LDL-DiI by 1.5-fold. The internalization of LDL-DiI was maximal at 60 μg of protein/ml (48 ± 8%). Scatchard analysis revealed a Kd of 3.2 ± 0.22 × 10−8 m and 2180 ± 190 binding sites in non-stimulated cells, a Kd of 7.73 ± 0.36 × 10−9 m and 12 500 ± 430 binding sites for IL-2 (100 U/ml)-stimulated cells, and a Kd of 7.2 ± 0.43 × 10−9 m and 13 250 ± 450 binding sites for PWM (1:200 dilution)-stimulated cells. Lineweaver–Burk analysis of LDL binding (LDL-DiI) revealed that the apparent Kd for non-stimulated cells was 1.3 ± 0.11 × 10−8 m, and 9.2 ± 0.2 × 10−9 m and 7.5 ± 0.25 × 10−9 m for IL-2- and PWM-stimulated cells, respectively. B lymphocytes from tonsils also showed a high expression of LDLR assessed with anti-LDLR (70 ± 6%). The high expression of LDLR and the avid internalization of LDL suggest that LDL may be important for B cell physiological responses