Corrections and Retraction CORRECTIONS RETRACTION EVOLUTION IMMUNOLOGY Correction for “Phylogenomic analyses reveal convergent pat- Retraction for “B7-DC cross-linking restores antigen uptake terns of adaptive evolution in elephant and human ancestries,” by and augments antigen-presenting cell function by matured den- Morris Goodman, Kirstin N. Sterner, Munirul Islam, Monica dritic cells” by Suresh Radhakrishnan, Esteban Celis, and Larry Uddin, Chet C. Sherwood, Patrick R. Hof, Zhuo-Cheng Hou, R. Pease, which appeared in issue 32, August 9, 2005, of Proc Natl Leonard Lipovich, Hui Jia, Lawrence I. Grossman, and Derek E. Acad Sci USA (102:11438–11443; first published online August 1, Wildman, which appeared in issue 49, December 8, 2009, of Proc 2005; doi: 10.1073/pnas.0501420102). The authors wish to note the Natl Acad Sci USA (106:20824–20829; first published November following: “After a re-examination of key findings underlying the 19, 2009; 10.1073/pnas.0911239106). reported conclusions that B7-DCXAb is an immune modulatory The authors note that the incorrect URL for accessing the reagent, we no longer believe this is the case. Using blinded pro- data in the Dryad database was published. The data discussed in tocols we re-examined experiments purported to demonstrate the this publication have been deposited in the Dryad Digital activation of dendritic cells, activation of cytotoxic T cells, induc- Repository database: http://hdl.handle.net/10255/dryad.908. tion of tumor immunity, modulation of allergic responses, breaking tolerance in the RIP-OVA diabetes model, and the reprogramming www.pnas.org/cgi/doi/10.1073/pnas.1003435107 of Th2 and T regulatory cells. Some of these repeated studies were direct attempts to reproduce key findings in the manuscript cited MEDICAL SCIENCES above. In no case did these repeat studies reveal any evidence that the B7-DCXAb reagent had the previously reported activity. In the Correction for “Sensitivity of MRI resonance frequency to the course of this re-examination, we were able to study all the anti- orientation of brain tissue microstructure,” by Jongho Lee, Karin bodies used in the various phases of our work spanning the last Shmueli, Masaki Fukunaga, Peter van Gelderen, Hellmut Merkle, 10 years. None of these antibodies appears to be active in any of our Afonso C. Silva, and Jeff H. Duyn, which appeared in issue 11, Proc Natl Acad Sci USA – fi repeat assays. We do not believe something has happened recently March 16, 2010, of (107:5130 5135; rst to the reagent changing its potency. Therefore, the authors seek to published March 2, 2010; 10.1073/pnas.0910222107). ” ’ retract this work. The authors note that due to a printer s error in adding an Suresh Radhakrishnan additional reference in the proof, beginning with the second ci- fi Esteban Celis tation for reference 12 on page 5130, right column, rst para- Larry R. Pease graph, fifth line, all numerical references should have appeared as one number higher, e.g., reference 12 becomes reference 13. www.pnas.org/cgi/doi/10.1073/pnas.1003319107 This is with the exception of reference 1 on page 5133, left column, last paragraph, fifth line. www.pnas.org/cgi/doi/10.1073/pnas.1003440107 NEUROSCIENCE Correction for “Phosphorylation of Rap1GAP, a striatally en- riched protein, by protein kinase A controls Rap1 activity and dendritic spine morphology,” by Thomas McAvoy, Ming-ming Zhou, Paul Greengard, and Angus C. Nairn, which appeared in issue 9, March 3, 2009, of Proc Natl Acad Sci USA (106:3531–3536; first published February 13, 2009; 10.1073/pnas.0813263106). The authors note that in the abstract of their paper, the sen- tence, “Phosphorylation of Rap1GAP is also associated with in- creased dendritic spine head size in cultured neurons” should instead appear as “Phosphorylation of Rap1GAP is also asso- ciated with decreased dendritic spine head size in cultured neu- rons.” This error does not affect the conclusions of the article. www.pnas.org/cgi/doi/10.1073/pnas.1003564107 8498 | PNAS | May 4, 2010 | vol. 107 | no. 18 www.pnas.org Downloaded by guest on September 24, 2021 Sensitivity of MRI resonance frequency to the orientation of brain tissue microstructure Jongho Leea,1, Karin Shmuelia, Masaki Fukunagaa, Peter van Gelderena, Hellmut Merklea, Afonso C. Silvab, and Jeff H. Duyna aAdvanced MRI Section and bCerebral Microcirculation Unit, Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892 Edited* by Adriaan Bax, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD, and approved January 22, 2010 (received for review September 29, 2009) Recent advances in high-field (≥7 T) MRI have made it possible to tissue microstructure and its orientation relative to the main study the fine structure of the human brain at the level of fiber bun- magnetic field. The authors applied the Lorentzian cavity concept dles and cortical layers. In particular, techniques aimed at detecting (11, 12) to estimate the magnetic field induced by microscopic MRI resonance frequency shifts originating from local variation variations in magnetic susceptibilities. Using a nonspherical in magnetic susceptibility and other sources have greatly improved Lorentzian cavity, proposed earlier in (12, 13), to model the the visualization of these structures. A recent theoretical study [He X, compartmentalization of water protons in an anisotropic tissue Yablonskiy DA (2009) Proc Natl Acad Sci USA 106:13558–13563] sug- structure, the authors suggested the presence of a net (voxel- gests that MRI resonance frequency may report not only on tissue averaged) frequency shift that depends on the tissue’s orientation composition, but also on microscopic compartmentalization of sus- in the externally applied magnetic field. This mechanism could ceptibility inclusions and their orientation relative to the magnetic explain some of the strong frequency shifts observed in the major field. The proposed sensitivity to tissue structure may greatly expand fiber bundles (Fig. 1) and may have important implications for the the information available with conventional MRI techniques. To in- application and interpretation of the resonance frequency in vestigate this possibility, we studied postmortem tissue samples from GRE MRI. human corpus callosum with an experimental design that allowed The extent to which the Lorentzian cavity concept, which is separation of microstructural effects from confounding macrostruc- well established at the atomic (nanometer) scale for electric and MEDICAL SCIENCES tural effects. The results show that MRI resonance frequency does magnetic fields (11, 14), should be used to account for the field depend on microstructural orientation. Furthermore, the spatial dis- distributions at larger (micrometer) scales that may be present in tribution of the resonance frequency shift suggests an origin related brain structures is not clear, however. Furthermore, the exper- to anisotropic susceptibility effects rather than microscopic compart- imental evidence is sparse in the aforementioned study (9), and mentalization. This anisotropy, which has been shown to depend on interpretation of the results is confounded by large-scale geo- molecular ordering, may provide valuable information about tissue metric effects inherent to the susceptibility-related contrast molecular structure. mechanism. The purpose of the current study was to further investigate MRI phase contrast | resonance frequency shift | anisotropic susceptibility | the potential effect of brain microstructure on MRI resonance magnetic susceptibility tensor | white matter fiber tracking frequency. Results ecent high-field (≥7 T) human MRI studies have demon- Rstrated that contrast based on resonance frequency shifts The effect of tissue microstructure on MRI resonance frequency may substantially improve the visualization of fine-scale struc- was investigated by manipulating microstructure while minimally tural variation in the human brain. For example, many of the affecting macrostructure. Experiments were performed on an brain’s major white matter fiber bundles and distinct cortical elongated section of human corpus callosum, a major white lamination patterns have recently been visualized in vivo by matter fiber bundle of the human brain. A part of the corpus observing the signal phase that is proportional to the resonance callosum was chosen that had relatively uniform (micro- frequency in gradient-echo (GRE) MRI (1–4). Despite this structural) fiber orientation, with fibers running mostly parallel achievement and the potential clinical and scientific significance, to the long direction of the section (Fig. 2A). The section was cut however, the mechanisms underlying magnetic resonance fre- into five subsections, which were aligned parallel to the MRI fi quency shifts remain poorly understood. main magnetic eld (B0) in a sample holder. The section was Several candidate mechanisms have been suggested and imaged under two conditions: one in which all subsections were investigated as sources for this frequency contrast (1, 5–8). A placed in their original orientation (condition A; Fig. 2C), and the primary candidate is an altered bulk magnetic susceptibility due other in which two of the subsections (C2 and C4) were rotated by D fi to such compounds as ferritin, myelin, and deoxyhemoglobin, all 90 degrees relative to B0 (condition B; Fig. 2 ). Microscopic ber fi of which are found throughout brain tissue. Strong support for orientation