Efficient Germinal Center Support Requires Tfh Expression of Alpha V Integrins

Thesis (Ph.D.)--University of Rochester. School of Medicine & Dentistry. Dept. of Microbiology and Immunology, 2018.CD4+ T cells receive various signals and cues from their microenvironment that guide their differentiation and function as immune effectors. These signals are often crucial for shaping an immune response that is appropriate and sufficient to eliminate the causal pathogen. Many cell types rely heavily on signals provided by the extracellular matrix (ECM) for their survival, positioning, and function. Despite this, little is known about how CD4+ T cells interact with the ECM in vivo and how those interactions contribute to an immune response. The ECM in peripheral tissues as well as in secondary lymphoid organs (SLO) undergoes significant changes in structure and composition during inflammation. In addition, CD4+ T cells express a number of receptors that may be sensitive to these changes. The aim of this thesis is to evaluate how CD4+ T cells interact with the ECM and what consequences these interactions have for the immune response at large. Previous work in our lab has established that CD4+ T cells in the dermis are dependent on alpha V integrins for migration. As such, we chose to examine the role of these integrins and their RGD-containing ligands in CD4+ T cell function and positioning in the lymph node. In concert with changes in the overall structure of the ECM, RGD-containing ligands were observed to accumulate substantially during inflammation in the skin. Surprisingly, alpha V-deficient CD4+ T cells showed reduced activation capacity and cytokine production in vitro, suggesting that interaction with the ECM or a cell surface alpha V ligand may contribute to naïve cell activation and differentiation. However, compensatory mechanisms appeared to be at play in vivo allowing normal cytokine responses to inflammation. In contrast to the generalized ECM deposition observed in the skin, a spatially distinct accumulation of RGD-containing ligands was seen in the skin-draining lymph node after immunization. The alpha V ligands vitronectin, osteopontin, and MFG-E8 were detected in close proximity to the GL7+ germinal centers of the B cell follicles. Interestingly, these ECM ligands were associated with CD35+ follicular dendritic cells (FDCs) and were often concentrated in the GC light zone. Evaluation of the B cell response showed an overall reduction in GC formation resulting in lower antigen-specific antibody production, reduced affinity maturation, and poor seeding of long-lived cells to the bone marrow when CD4+ T cells lacked alpha V integrins. Surprisingly, Tfh populations appeared normal and our experiments indicated that alpha V-deficient T cells are capable of providing B cell help in vitro. Histological analysis revealed that, while alpha V-deficient T cells were present in the B cell follicles, they failed to accumulate in the alpha V ligand-rich GC light zone to the same degree as WT cells

The Actin Cytoskeleton Responds to Inflammatory Cues and Alters Macrophage Activation

Much remains to be learned about the molecular mechanisms underlying a class of human disorders called actinopathies. These genetic disorders are characterized by loss-of-function mutations in actin-associated proteins that affect immune cells, leading to human immunopathology. However, much remains to be learned about how cytoskeletal dysregulation promotes immunological dysfunction. The current study reveals that the macrophage actin cytoskeleton responds to LPS/IFNγ stimulation in a biphasic manner that involves cellular contraction followed by cellular spreading. Myosin II inhibition by blebbistatin blocks the initial contraction phase and lowers iNOS protein levels and nitric oxide secretion. Conversely, conditional deletion of Arp2/3 complex in macrophages attenuates spreading and increases nitric oxide secretion. However, iNOS transcription is not altered by loss of myosin II or Arp2/3 function, suggesting post-transcriptional regulation of iNOS by the cytoskeleton. Consistent with this idea, proteasome inhibition reverses the effects of blebbistatin and rescues iNOS protein levels. Arp2/3-deficient macrophages demonstrate two additional phenotypes: defective MHCII surface localization, and depressed secretion of the T cell chemokine CCL22. These data suggest that interplay between myosin II and Arp2/3 influences macrophage activity, and potentially impacts adaptive-innate immune coordination. Disrupting this balance could have detrimental impacts, particularly in the context of Arp2/3-associated actinopathies