stimulation with anti-CD3 + anti-CD28 antibodies. Althoughdetected in spleen and lymph nodes, MDSC were onlysuppressive in blood and bone marrow. The suppressionwas contact-dependant and mediated by the action ofinhibitor of inducible nitric oxide synthase (iNOS).Western blot analyses revealed that iNOS was expressedonly after contact between MDSC and activated effector Tcells. Interestingly, iNOS was expressed to a much lesserextent after contact with activated CD4+CD25high T regcells and their induced proliferation and released of IFNγwas not inhibited by MDSC. In vivo, the expression of iNOSwas higher in the blood and in the graft of tolerantrecipients as compared with isografted recipients. Inaddition, the injection in tolerant animals of aminogua-nidine, which inhibits iNOS, induced graft rejection within3 weeks. In conclusion, these results suggest that MDSC,accumulated in the blood of tolerant kidney recipients,release high levels of NO after contact with activatedeffector T cells and specifically control their proliferativeresponse.

doi:10.1016/j.clim.2008.03.032

OR.28. Macrophages Remember Neural Signalsthat Teach Attenuation of Responses toBacterial EndotoxinWilliam Parrish, M. Ochani, M. Rosas-Ballina,M. Gallowitsch-Puerta, Houman Khalili, A. Damle, Y. Harris,K. Ochani, Xinchun Lin, E. Miller, Jared Huston, ChristopherCzura, Wentian Li, F. Batliwalla, Peter Gregersen, KevinTracey. Feinstein Institute for Medical Research, Manhasset,NY

Macrophage cytokine production is inhibited by vagusnerve signals that are transduced through the α7 nicotinicacetylcholine receptor subunit (α7nAChR) dependent path-way termed the “cholinergic anti-inflammatory pathway”(Nature 420:853-9, 2002). Here we address the hypothesisthat macrophages can “remember” the anti-inflammatorystimulus provided by vagus nerve signals. Vagus nervestimulation (VNS) (5V, 2 ms, 1 Hz, 2.5 min) in rats 24 h priorto endotoxin (LPS) (1 mg/Kg I.P.) significantly reducedserum TNF (sham=767 pg/ml; VNS=358 pg/ml, pb0.01).This TNF-suppressing effect persists even when endotoxinexposure is delayed for 48 h after VNS (sham TNF = 1327;VNS TNF = 824, pb0.05). The molecular mechanism isattributable to α7nAChR signaling, because VNS fails toreduce TNF levels in α7nAChR KO mice. This cellularmemory can be recapitulated in human macrophagecultures pulsed with acetylcholine (100 μM Ach; 60 minpulse; 24 h prior to LPS). LPS-induced TNF release wasreduced 54% as compared with vehicle controls (pb0.05);pulsing also significantly suppressed activation of NF-κB(74%). ACh-pulsing significantly altered the macrophagetranscriptome response to endotoxin (498 differentiallyexpressed genes, pb0.01), indicating that suppressedmacrophage TNF responses following cholinergic stimula-tion persist as a memory-like response. Evidence thatdiscrete neural signals can mediate memory responses inmacrophages via α7nAChR has surprising implications for

understanding innate immunity. Supported in part byNIGMS.

doi:10.1016/j.clim.2008.03.033

OR.29. Role of Scavenger Receptors as EndocytoticReceptors forHumanHsp70 inMHCClass II-dependentAntigen PresentationNadja Fischer,1,3 Markus Haug,1 Rupert Handgretinger,1

Guenther E. Dannecker,2 Ursula Holzer.1 1University ofTuebingen, Tuebingen, Germany;

2Olgahospital, Stuttgart,

Germany; 3Institute for Cell Biology, Tuebingen, Germany

Stress inducible heat shock protein Hsp70 has beenfound to facilitate processing and presentation of MHCclass II-restricted antigens resulting in enhanced CD4+ Tcell activation. Prerequisite for this particular biologicalproperty of heat shock proteins (HSPs) is a receptor-mediated endocytosis of the Hsp70:antigen complex by theantigen presenting cells (APCs). So far scavenger receptorsespecially LOX-1 and CD91 are postulated to be the mainHSP binding structures on murine and human APCs. Inorder to further identify HSP-binding structures expressedon the surface of human APCs which are involved in MHCclass II presentation of HSP-bound antigens we have usedshort interfering RNA to knockdown postulated HSP-receptors. Antigen uptake and presentation ability ofgenerated APCs was compared to untreated APCs inproliferation experiments with human antigen-specificCD4+ T cells. APCs were incubated with either antigenicpeptide alone or with peptide:Hsp70 complexes andsubsequent co-cultured for six days with CD4+ T cells.CFSE-labeled CD4+ T cells were stained with peptide-loaded HLA-DR tetramers to allow quantification ofproliferated antigen-specific CD4+ T cells. Expression ofscavenger receptors was observed to correlate with theability of APCs to present Hsp70-chaperoned peptides. Anenhanced immunogenicity of MHC class II restrictedpeptide:Hsp70 complexes was only seen in experimentswith untreated cells. These results confirm in a humanantigen-specific setting the essential role of scavengerreceptors (CD91, LOX-1) as endocytotic receptors forHsp70 in MHC class II-dependent antigen presentation.

doi:10.1016/j.clim.2008.03.034

OR.30. T Cell Sensing of Antigen Dose GovernsInteractive Behavior with Dendritic Cells and Sets aThreshold for T Cell ActivationSarah Henrickson,1 Thorsten Mempel,1 Irina Mazo,1 Bai Liu,2

Maksym Artomov,3 Huan Zheng,3 Antonio Peixoto,1 MichaelFlynn,1 Balimkiz Senman,1 Tobias Junt,1 Hing Wong,2 ArupChakraborty,3 Ulrich von Andrian.1 1Harvard MedicalSchool, Boston, MA;

2Altor BioSciences, Miramar, FL;

3MIT,

Cambridge, MA

The rules by which naive T cells decide whether to andhow to respond to antigenic stimuli are not completely

S13Abstracts