Daniel C. Bullard

Bio: Daniel C. Bullard is an academic researcher from University of Alabama at Birmingham. The author has contributed to research in topics: Selectin & Cell adhesion molecule. The author has an hindex of 46, co-authored 103 publications receiving 10745 citations. Previous affiliations of Daniel C. Bullard include Baylor College of Medicine & Case Western Reserve University.

Transforming growth factor-beta induces development of the T(H)17 lineage.

Abstract: A new lineage of effector CD4+ T cells characterized by production of interleukin (IL)-17, the T-helper-17 (T(H)17) lineage, was recently described based on developmental and functional features distinct from those of classical T(H)1 and T(H)2 lineages. Like T(H)1 and T(H)2, T(H)17 cells almost certainly evolved to provide adaptive immunity tailored to specific classes of pathogens, such as extracellular bacteria. Aberrant T(H)17 responses have been implicated in a growing list of autoimmune disorders. T(H)17 development has been linked to IL-23, an IL-12 cytokine family member that shares with IL-12 a common subunit, IL-12p40 (ref. 8). The IL-23 and IL-12 receptors also share a subunit, IL-12Rbeta1, that pairs with unique, inducible components, IL-23R and IL-12Rbeta2, to confer receptor responsiveness. Here we identify transforming growth factor-beta (TGF-beta) as a cytokine critical for commitment to T(H)17 development. TGF-beta acts to upregulate IL-23R expression, thereby conferring responsiveness to IL-23. Although dispensable for the development of IL-17-producing T cells in vitro and in vivo, IL-23 is required for host protection against a bacterial pathogen, Citrobacter rodentium. The action of TGF-beta on naive T cells is antagonized by interferon-gamma and IL-4, thus providing a mechanism for divergence of the T(H)1, T(H)2 and T(H)17 lineages.

Sequential contribution of L- and P-selectin to leukocyte rolling in vivo.

Abstract: Leukocyte recruitment into inflammatory sites is initiated by a reversible transient adhesive contact with the endothelium called leukocyte rolling, which is thought to be mediated by the selectin family of adhesion molecules. Selectin-mediated rolling precedes inflammatory cell emigration, which is significantly impaired in both P- and L-selectin gene-deficient mice. We report here that approximately 13% of all leukocytes passing venules of the cremaster muscle of wild-type mice roll along the endothelium at < 20 min after surgical dissection. Rolling leukocyte flux fraction reaches a maximum of 28% at 40-60 min and returns to 13% at 80-120 min. In P-selectin-deficient mice, rolling is absent initially and reaches 5% at 80-120 min. Rolling flux fraction in L-selectin-deficient mice is similar to wild type initially and declines to 5% at 80-120 min. In both wild-type and L-selectin-deficient mice, initial leukocyte rolling (0-60 min) is completely blocked by the P-selectin monoclonal antibody (mAb) RB40.34, but unaffected by L-selectin mAb MEL-14. Conversely, rolling at later time points (60-120 min) is inhibited by mAb MEL-14 but not by mAb RB40.34. After treatment with tumor necrosis factor (TNF)-alpha for 2 h, approximately 24% of all passing leukocytes roll in cremaster venules of wild-type and P-selectin gene-deficient mice. Rolling in TNF-alpha-treated mice is unaffected by P-selectin mAb or E-selectin mAb 10E9.6. By contrast, rolling in TNF-alpha-treated P-selectin-deficient mice is completely blocked by L-selectin mAb. These data show that P-selectin is important during the initial induction of leukocyte rolling after tissue trauma. At later time points and in TNF-alpha-treated preparations, rolling is largely L-selectin dependent. Under the conditions tested, we are unable to find evidence for involvement of E-selectin in leukocyte rolling in mice.

Decreased resistance to bacterial infection and granulocyte defects in IAP-deficient mice

Abstract: Granulocyte [polymorphonuclear leucocyte (PMN)] migration to sites of infection and subsequent activation is essential for host defense. Gene-targeted mice deficient for integrin-associated protein (IAP, also termed CD47) succumbed to Escherichia coli peritonitis at inoccula survived by heterozygous littermates. In vivo, they had an early defect in PMN accumulation at the site of infection. In vitro, IAP-/- PMNs were deficient in beta3 integrin-dependent ligand binding, activation of an oxidative burst, and Fc receptor-mediated phagocytosis. Thus, IAP plays a key role in host defense by participating both in PMN migration in response to bacterial infection and in PMN activation at extravascular sites.

Relative Contribution of LFA-1 and Mac-1 to Neutrophil Adhesion and Migration

Abstract: To differentiate the unique and overlapping functions of LFA-1 and Mac-1, LFA-1-deficient mice were developed by targeted homologous recombination in embryonic stem cells, and neutrophil function was compared in vitro and in vivo with Mac-1-deficient, CD18-deficient, and wild-type mice. LFA-1-deficient mice exhibit leukocytosis but do not develop spontaneous infections, in contrast to CD18-deficient mice. After zymosan-activated serum stimulation, LFA-1-deficient neutrophils demonstrated activation, evidenced by up-regulation of surface Mac-1, but did not show increased adhesion to purified ICAM-1 or endothelial cells, similar to CD18-deficient neutrophils. Adhesion of Mac-1-deficient neutrophils significantly increased with stimulation, although adhesion was lower than for wild-type neutrophils. Evaluation of the strength of adhesion through LFA-1, Mac-1, and CD18 indicated a marked reduction in firm attachment, with increasing shear stress in LFA-1-deficient neutrophils, similar to CD18-deficient neutrophils, and only a modest reduction in Mac-1-deficient neutrophils. Leukocyte influx in a subcutaneous air pouch in response to TNF-alpha was reduced by 67% and 59% in LFA-1- and CD18-deficient mice but increased by 198% in Mac-1-deficient mice. Genetic deficiencies demonstrate that both LFA-1 and Mac-1 contribute to adhesion of neutrophils to endothelial cells and ICAM-1, but adhesion through LFA-1 overshadows the contribution from Mac-1. Neutrophil extravasation in response to TNF-alpha in LFA-1-deficient mice dramatically decreased, whereas neutrophil extravasation in Mac-1-deficient mice markedly increased.

A minimal role for selectins in the recruitment of leukocytes into the inflamed liver microvasculature.

Abstract: A two-step paradigm for leukocyte recruitment has been established in a number of tissues including the mesentery, skin, and muscle, and necessitates an initial rolling step via the selectins before firm leukocyte adhesion via the integrins. In view of the many inflammatory diseases that involve the liver, we investigated the importance of rolling and the selectins in the hepatic microvasculature and compared the responses to that of the commonly used mesentery or cremaster microvasculature. We visualized the liver microvasculature using intravital microscopy and we determined that within the liver the majority of leukocytes adhere within the sinusoids (80%) in response to a chemotactic stimulus such as FMLP (20% in postsinusoidal venules) whereas leukocytes adhere exclusively within postcapillary venules in tissue like the mouse cremaster. In the sinusoids, the adhesive response to FMLP is not dependent upon selectins inasmuch as adhesion was not reduced in the sinusoidal vessels of P-selectin-deficient mice or E-selectin/P-selectin- deficient animals in the presence or absence of L-selectin antibody. No rolling or adhesion was detected in response to FMLP in the selectin-deficient cremaster microvasculature. Immunoneutralization of selectins with fucoidan in wildtype mice eliminated rolling and adhesion in the cremaster but failed to affect adhesion in the liver sinusoids in response to FMLP. More long-term leukocyte recruitment with lipopolysaccharide (4 h) was also impaired in the cremaster but not the liver microvasculature in selectin-deficient animals. Leukocyte adhesion in the sinusoids was reduced in P-selectin-deficient mice also lacking intercellular adhesion molecule-1 (ICAM-1). This study for the first time demonstrates that selectins are not an essential step for leukocyte recruitment into the inflamed liver microvasculature.

Exploring the full spectrum of macrophage activation.

Abstract: Macrophages display remarkable plasticity and can change their physiology in response to environmental cues. These changes can give rise to different populations of cells with distinct functions. In this Review we suggest a new grouping of macrophage populations based on three different homeostatic activities - host defence, wound healing and immune regulation. We propose that similarly to primary colours, these three basic macrophage populations can blend into various other 'shades' of activation. We characterize each population and provide examples of macrophages from specific disease states that have the characteristics of one or more of these populations.

IL-17 and Th17 Cells.

Abstract: CD4+ T cells, upon activation and expansion, develop into different T helper cell subsets with different cytokine profiles and distinct effector functions. Until recently, T cells were divided into Th1 or Th2 cells, depending on the cytokines they produce. A third subset of IL-17-producing effector T helper cells, called Th17 cells, has now been discovered and characterized. Here, we summarize the current information on the differentiation and effector functions of the Th17 lineage. Th17 cells produce IL-17, IL-17F, and IL-22, thereby inducing a massive tissue reaction owing to the broad distribution of the IL-17 and IL-22 receptors. Th17 cells also secrete IL-21 to communicate with the cells of the immune system. The differentiation factors (TGF-β plus IL-6 or IL-21), the growth and stabilization factor (IL-23), and the transcription factors (STAT3, RORγt, and RORα) involved in the development of Th17 cells have just been identified. The participation of TGF-β in the differentiation of Th17 cells places ...

Neutrophil recruitment and function in health and inflammation

Abstract: Neutrophils have traditionally been thought of as simple foot soldiers of the innate immune system with a restricted set of pro-inflammatory functions. More recently, it has become apparent that neutrophils are, in fact, complex cells capable of a vast array of specialized functions. Although neutrophils are undoubtedly major effectors of acute inflammation, several lines of evidence indicate that they also contribute to chronic inflammatory conditions and adaptive immune responses. Here, we discuss the key features of the life of a neutrophil, from its release from bone marrow to its death. We discuss the possible existence of different neutrophil subsets and their putative anti-inflammatory roles. We focus on how neutrophils are recruited to infected or injured tissues and describe differences in neutrophil recruitment between different tissues. Finally, we explain the mechanisms that are used by neutrophils to promote protective or pathological immune responses at different sites.