STAT1-regulated lung MDSC-like cells produce IL-10 and efferocytose apoptotic neutrophils with relevance in resolution of bacterial pneumonia.

Bacterial pneumonia remains a significant burden worldwide. Although an inflammatory response in the lung is required to fight the causative agent, persistent tissue-resident neutrophils in non-resolving pneumonia can induce collateral tissue damage and precipitate acute lung injury. However, little is known about mechanisms orchestrated in the lung tissue that remove apoptotic neutrophils to restore tissue homeostasis. In mice infected with Klebsiella pneumoniae, a bacterium commonly associated with hospital-acquired pneumonia, we show that interleukin (IL)-10 is essential for resolution of lung inflammation and recovery of mice after infection. Although IL-10(-/-) mice cleared bacteria, they displayed increased morbidity with progressive weight loss and persistent lung inflammation in the later phase after infection. A source of tissue IL-10 was found to be resident CD11b(+)Gr1(int)F4/80(+) cells resembling myeloid-derived suppressor cells (MDSCs) that appeared with a delayed kinetics after infection. These cells efficiently efferocytosed apoptotic neutrophils, which was aided by IL-10. The lung neutrophil burden was attenuated in infected signal transducer and activator of transcription 1 (STAT1)(-/-) mice with concomitant increase in the frequency of the MDSC-like cells and lung IL-10 levels. Thus, inhibiting STAT1 in combination with antibiotics may be a novel therapeutic strategy to address inefficient resolution of bacterial pneumonia.

Red cell microparticle enumeration: validation of a flow cytometric approach.

BACKGROUND AND OBJECTIVES: There is growing interest in the clinical application of red blood cell (RBC) microparticle (MP) enumeration as they have been postulated to be effectors of coagulation and inflammation following transfusion and in sickle cell disease. No uniform approach in MP enumeration exists and a key limitation is the lack of an internal validation process. We present and validate a flow cytometric approach where an internal standard is utilized. MATERIALS AND METHODS: Glycophorin A(+) Annexin V(+) events were enumerated using MPs isolated from RBC units or plasma samples obtained from volunteers. A mixture of absolute counting (7·6 µm) and calibration beads (0·5, 0·9 and 3 µm) at a fixed ratio was added to each sample. RESULTS: RBC MPs were initially selected based upon a fluorescence threshold, and the 0·5- and 0·9-µm beads defined the upper and lower light scatter distribution of MPs. The ratio of 7·6:3-µm bead events was used as an internal standard to validate the precision of MP enumeration across samples (coefficient of variation = 2·5-7·2%) and remained constant in both platelet-rich plasma (PRP) and platelet-free plasma (PFP). RBC MP counts increased in both PRP and PFP obtained from whole blood stimulated with ionophore and increasing calcium concentrations, with PRP showing higher MP counts than PFP at every concentration studied. CONCLUSION: This method is a useful strategy to detect RBC MP counts across bio-samples provided that the flow cytometer can reliably discriminate the size of the calibration beads.

TLR4/MyD88-induced CD11b+Gr-1 int F4/80+ non-migratory myeloid cells suppress Th2 effector function in the lung.

In humans, environmental exposure to a high dose of lipopolysaccharide (LPS) protects from allergic asthma, the immunological underpinnings of which are not well understood. In mice, exposure to a high LPS dose blunted house dust mite-induced airway eosinophilia and T-helper 2 (Th2) cytokine production. Although adoptively transferred Th2 cells induced allergic airway inflammation in control mice, they were unable to do so in LPS-exposed mice. LPS promoted the development of a CD11b(+)Gr1(int)F4/80(+) lung-resident cell resembling myeloid-derived suppressor cells in a Toll-like receptor 4 and myeloid differentiation factor 88 (MyD88)-dependent manner that suppressed lung dendritic cell (DC)-mediated reactivation of primed Th2 cells. LPS effects switched from suppressive to stimulatory in MyD88(-/-) mice. Suppression of Th2 effector function was reversed by anti-interleukin-10 (IL-10) or inhibition of arginase 1. Lineage(neg) bone marrow progenitor cells could be induced by LPS to develop into CD11b(+)Gr1(int)F4/80(+)cells both in vivo and in vitro that when adoptively transferred suppressed allergen-induced airway inflammation in recipient mice. These data suggest that CD11b(+)Gr1(int)F4/80(+) cells contribute to the protective effects of LPS in allergic asthma by tempering Th2 effector function in the tissue.

Distinct autoreactive T cell responses to native and fragmented DNA topoisomerase I: influence of APC type and IL-2.

Systemic sclerosis (SSc) is an autoimmune connective tissue disease of unknown etiology in which T cell responses to various autoantigens, including DNA topoisomerase I (Topo I), have been implicated. We investigated whether dendritic cells, generally considered to be the most potent APCs for the initiation of immune responses, would present either of two forms of Topo I to T cells more efficiently than PBMC APCS: Using cells from healthy controls and SSc patients, several important observations were made. First, neither APC type was able to initiate T cell proliferative responses to full-length native Topo I unless exogenous IL-2 was added. This is in contrast to vigorous T cell proliferation in response to Topo I polypeptide fragments presented by either APC type. Second, T cell responses to the full-length form of Topo I presented by dendritic cells were considerably lower than responses to Ag presented by PBMC APCS: Finally, no secondary T cell responses were observed unless the same Ag/APC combination as that used in the primary stimulation was maintained. These data indicate that different peptides are generated based upon the form of the Topo I and the APC that processes it. Taken together, these results suggest that a very specific combination of antigenic form and APC may be involved in breaking tolerance to Topo I in the early stages of development of SSC:

Evidence of positive cross-regulation on Th1 by Th2 and antigen-presenting cells: effects on Th1 induced by IL-4 and IL-12.

The response of Th cells to cytokines is normally strictly regulated, such that following antigenic stimulation, Th cells respond for only a short period of time, after which they become refractory to cytokine-mediated effects. IL-12, a costimulator of Th1 having no proliferation-inducing capacity of its own, allows Th1 clones and lines to respond to IL-4 when they would otherwise be unable to respond to this cytokine. Cells that have proliferated in response to IL-4 plus IL-12 are fully able to be subsequently activated by specific Ag and APC. Additionally, the response to IL-4 of Th1 effector cells derived from normal murine spleen is enhanced significantly by IL-12. Furthermore, in the presence of IL-12, stimulated Th2 can induce proliferation of Th1 via IL-4 production, in a dual chamber culture system. We hypothesize that the effects of IL-4 and IL-12 represent a novel, positive cross-regulatory pathway that acts on Th1, and is mediated by Th2 (the IL-4 source) and APC (the IL-12 source). We propose this as a way for a Th2 immune response to positively influence an ongoing or waning Th1 response.

Crossregulation between Th1 and Th2 cells.

Th1 and Th2 subsets have been characterized on the basis of the cytokines they secrete and the immune functions they mediate. Th1 cells secrete IL-2, IFN-gamma, and lymphotoxin and are important in the cell-mediated response; Th2 cells secrete IL-4, IL-5, IL-10, and IL-13 and are important in the control of macrophage function and in the stimulation of particular immunoglobulin isotypes. Cytokines secreted by Th1 and Th2 cells regulate the growth and differentiation of Th1 and Th2 cells in both positive and negative ways; this has been termed crossregulation. Much work has concentrated on the factors important in the differentiation of these Th subsets, and it has been established that Th cells become committed to a Th1 or Th2 phenotype within 48 hrs of antigenic stimulation. During the differentiation process irreversible changes in the expression and function of cytokine receptors occur that provide an explanation for the observed crossregulatory features of Th1 and Th2 cells. In this review we summarize the crossregulation between Th1 and Th2 cells in terms of the changes in cytokine receptor expression and function that occur during differentiation.

Modeling the proliferative response of T cells to IL-2 and IL-4.

Interleukin (IL) -2 and IL-4 are growth factors for both T and B cells. When both cytokines are present, synergy is observed in some cases and antagonism in others. The studies presented here describe the use of a detailed mathematical model for the proliferative response of the T cell line, HT-2. This cell line responds to IL-2 and to IL-4 and shows a synergistic response when both cytokines are present. This model incorporates the observed synergy between these two cytokines while at the same time incorporating the known down-regulatory effect of IL-4 on the number of IL-2 receptors (IL-2R) at the cell surface, and it is able to reproduce a variety of experimental data. The major results from these studies include the following: the observation that the binding of IL-4 to its receptor is 1/10 as effective in delivering a proliferative signal as IL-2 binding to its receptor, the determination of the threshold number of bindings required to signal proliferation stimulated by IL-2 and IL-4, the demonstration that many different sets of experimental data can be accurately modeled, and the use of simple parameter terms to model the synergy between IL-2 and IL-4.

Crossregulation between T helper cell (Th)1 and Th2: inhibition of Th2 proliferation by IFN-gamma involves interference with IL-1.

The Th1-derived cytokine IFN-gamma inhibits the proliferation of Th2 lymphocytes, but the mechanism of inhibition is not known. Under certain disease conditions, an established Th2-mediated immune response is undesirable and a Th1-mediated response is beneficial. However, established Th2 cells appear to be phenotypically stable. Thus, learning more about cytokine-mediated regulation of established Th2 cells is important if deleterious immune responses are to be altered. We studied the effects of IFN-gamma on a panel of recently derived Th2 lines and clones, as well as a previously established Th2 clone, 13.26. Inhibition by IFN-gamma was observed only when there was a concomitant response to IL-1, a known costimulator of Th2. Clone 13.26 was particularly sensitive to both IL-1 and IFN-gamma, so it was studied in greater detail. We examined cytokine responses using stimulation by anti-TCR mAb-coated plates, or Ag presented by APC populations that do or do not produce IL-1. All IL-1-mediated proliferative responses of 13.26 were inhibited by IFN-gamma, whereas IL-1-independent (IL-4-associated) responses were unaffected. Our data suggest that IFN-gamma inhibits Th2 proliferation through an IL-1-dependent mechanism, and furthermore, that the costimulatory pathways used by APCs may be critical for subsequent Th cell responses to cytokines.

Generation of DC from mouse spleen cell cultures in response to GM-CSF: immunophenotypic and functional analyses.

In all tissues that have been studied to date, dendritic leucocytes constitute only a small proportion of total cells and are difficult both to isolate and purify. This study reports on a method for the propagation of large numbers of dendritic cells (DC) from mouse spleen using granulocyte-macrophage colony-stimulating factor (GM-CSF) and their characteristics. Within a few days of liquid culture in GM-CSF, B10 BR (H-2k, I-E+) mouse splenocytes formed loosely adherent myeloid cell clusters. Mononuclear progeny released from these clusters at and beyond 4 days exhibited distinct dendritic morphology and strongly expressed leucocyte common antigen (CD45), CD11b, heat-stable antigen, Pgp-1 (CD44) and intercellular adhesion molecule-1 (ICAM-1; CD54). The intensity of expression of the DC-restricted markers NLDC 145 and 33D1, the macrophage marker F4/80, and Fc gamma RII (CDw32) was low to moderate, whereas the cells were negative for CD3, CD45RA and NK1.1. High and moderate levels, respectively, of cell surface staining for major histocompatibility complex (MHC) class II (I-Ek) and the B7 antigens (counter-receptors of CTLA4, a structural homologue of CD28) were associated with potent stimulation of unprimed, allogeneic T cells (B10; H-2b, I-E-). DC propagated in a similar fashion from DBA/2 mouse spleen proved to be strong antigen-presenting cells (APC) for MHC-restricted, syngeneic T-helper type 2 (Th2) cell clones specifically responsive to sperm whale myoglobin. Footpad or intravenous injection of GM-CSF-stimulated B10.BR spleen-derived DC into B10 (H-2b, I-E-) recipients resulted in homing of the allogeneic cells to T-cell-dependent areas of lymph nodes and spleen, where they strongly expressed donor MHC class II antigen 1-2 days later. These findings indicate that cells can be propagated from fresh splenocyte suspensions that exhibit distinctive features of DC, namely morphology, motility, cell-surface phenotype, potent allogeneic and syngeneic APC function and in vivo homing ability. Propagation of DC in this manner from progenitors present in lymphoid tissue provides an alternative and relatively convenient source of high numbers of these otherwise difficult to isolate but functionally important APC.