Julie Ledford

Julie Ledford

Associate Professor, Cellular and Molecular Medicine
Associate Professor, Immunobiology
Associate Professor, Medicine
Associate Professor, Clinical Translational Sciences
Associate Professor, Applied BioSciences - GIDP
Member of the Graduate Faculty
Associate Professor, BIO5 Institute
Primary Department
Contact
(520) 626-0276

Work Summary

Julie Ledford's research focuses on respiratory disease, and genetic and molecular mechanisms of allergic airway diseases in children.

Research Interest

Dr. Ledford’s current work in the area of pulmonary surfactant immunobiology combines her knowledge of mouse genetics, pulmonary disease models and immune function regulation and focuses on understanding the role of Surfactant Protein-A (SP-A) and how it regulates signaling pathways within various immune cell populations. Specifically, she is interested in how SP-A regulates degranulation, either directly or indirectly, of two important cell types in asthma: mast cells and eosinophils. More recently, Dr. Ledford’s research has focused on understanding how genetic variation within human SP-A2 alters functionality of the protein in relation to eosinophil activities and how this translates to characteristics observed in human asthma.

Publications

Rabinowitz, J. E., Bowles, D. E., Faust, S. M., Ledford, J. G., Cunningham, S. E., & Samulski, R. J. (2004). Cross-dressing the virion: the transcapsidation of adeno-associated virus serotypes functionally defines subgroups. Journal of virology, 78(9), 4421-32.

For all adeno-associated virus (AAV) serotypes, 60 monomers of the Vp1, Vp2, and Vp3 structural proteins assemble via an unknown mechanism to form an intact capsid. In an effort to better understand the properties of the capsid monomers and their role in viral entry and infection, we evaluated whether monomers from distinct serotypes can be mixed to form infectious particles with unique phenotypes. This transcapsidation approach consisted of the transfection of pairwise combinations of AAV serotype 1 to 5 helper plasmids to produce mosaic capsid recombinant AAV (rAAV). All ratios (19:1, 3:1, 1:1, 1:3, and 1:19) of these mixtures were able to replicate the green fluorescent protein transgene and to produce capsid proteins. A high-titer rAAV was obtained with mixtures that included either serotype 1, 2, or 3, whereas an rAAV of intermediate titer was obtained from serotype 5 mixtures. Only mixtures containing the AAV4 capsid exhibited reduced packaging capacity. The binding profiles of the mixed-virus preparations to either heparin sulfate (HS) or mucin agarose revealed that only AAV3-AAV5 mixtures at the 3:1 ratio exhibited duality in binding. All other mixtures displayed either an abrupt shift or a gradual alteration in the binding profile to the respective ligand upon increase of a capsid component that conferred either HS or mucin binding. The transduction of cell lines was used to further evaluate the phenotypes of these transcapsidated virions. Three transduction profiles were observed: (i) small to no change regardless of ratio, (ii) a gradual increase in transduction consistent with titration of a second capsid component, or (iii) an abrupt increase in transduction (threshold effect) dependent on the specific ratios used. Interestingly, an unexpected synergistic effect in transduction was observed when AAV1 helper constructs were combined with type 2 or type 3 recipient helpers. Further studies determined that at least two components contributed to this observed synergy: (i) heparin-mediated binding from AAV2 and (ii) an unidentified enhancement activity from AAV1 structural proteins. Using this procedure of mixing different AAV helper plasmids to generate "cross-dressed" AAV virions, we propose an additional means of classifying new AAV serotypes into subgroups based on functional approaches to analyze AAV capsid assembly, receptor-mediated binding, and virus trafficking. Exploitation of this approach in generating custom-designed AAV vectors should be of significant value to the field of gene therapy.

Mukherjee, S., Giamberardino, C., Thomas, J., Evans, K., Goto, H., Ledford, J. G., Hsia, B., Pastva, A. M., & Wright, J. R. (2012). Surfactant protein A integrates activation signal strength to differentially modulate T cell proliferation. Journal of immunology (Baltimore, Md. : 1950), 188(3), 957-67.

Pulmonary surfactant lipoproteins lower the surface tension at the alveolar-airway interface of the lung and participate in host defense. Previous studies reported that surfactant protein A (SP-A) inhibits lymphocyte proliferation. We hypothesized that SP-A-mediated modulation of T cell activation depends upon the strength, duration, and type of lymphocyte activating signals. Modulation of T cell signal strength imparted by different activating agents ex vivo and in vivo in different mouse models and in vitro with human T cells shows a strong correlation between strength of signal (SoS) and functional effects of SP-A interactions. T cell proliferation is enhanced in the presence of SP-A at low SoS imparted by exogenous mitogens, specific Abs, APCs, or in homeostatic proliferation. Proliferation is inhibited at higher SoS imparted by different doses of the same T cell mitogens or indirect stimuli such as LPS. Importantly, reconstitution with exogenous SP-A into the lungs of SP-A(-/-) mice stimulated with a strong signal also resulted in suppression of T cell proliferation while elevating baseline proliferation in unstimulated T cells. These signal strength and SP-A-dependent effects are mediated by changes in intracellular Ca(2+) levels over time, involving extrinsic Ca(2+)-activated channels late during activation. These effects are intrinsic to the global T cell population and are manifested in vivo in naive as well as memory phenotype T cells. Thus, SP-A appears to integrate signal thresholds to control T cell proliferation.