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Although antigen-specific priming of antibody responses is impaired during sepsis, there is nevertheless a strong increase in IgM and IgG serum concentrations. Using colon ascendens stent peritonitis (CASP), a mouse model of polymicrobial abdominal sepsis, we observed substantial increases in IgM as well as IgG of all subclasses, starting at day 3 and peaking 2 weeks after sepsis induction. The dominant source of antibody-secreting cells was by far the spleen, with a minor contribution of the mesenteric lymph nodes. Remarkably, sepsis induction in splenectomized mice did not change the dynamics of the serum IgM/IgG reaction, indicating that the marginal zone B cells, which almost exclusively reside in the spleen, are dispensable in such a setting. Hence, in systemic bacterial infection, the function of the spleen as dominant niche of antibody-producing cells can be compensated by extra-splenic B cell populations as well as other lymphoid organs. Depletion of CD4+ T cells did not affect the IgM response, while it impaired IgG generation of all subclasses with the exception of IgG3. Taken together, our data demonstrate that the robust class-switched antibody response in sepsis encompasses both T cell-dependent and -independent components.
The immune system of all vertebrates primarily is responsible to maintain the organisms homeostasis by either eliminating neoplastic or altered body cells and to protect against foreign invaders (viruses, bacteria, fungi, parasites) (Murphy 2012). It is a highly regulated network of innate and adaptive mechanisms between humoral factors and leukocytes. The successful elimination or protection is crucially based on differentiation of self from non-self. Pathogens and altered body cells are recognized by different receptor complexes on immune cells. Expressed pathogen- or danger-associated molecular patterns (PAMPs or DAMPs, respectively) are bound by pattern recognition receptors (PRR) (Takeuchi and Akira 2010). Missing major histocompatibility (MHC) class I molecules or non-self (e.g. allogeneic or xenogeneic cells) MHC are recognized by natural killer cell receptors (Fischer, Koppang and Nakanishi 2013, Raulet 2006). Foreign non-self peptides are presented through MHC class I (intracellular) or through MHC class II (extracellular) to B- cell or T cell receptor complexes. This initial activation is regulated by humoral factors or cellular interactions (receptor-ligand interactions) resulting in the activation, proliferation and effector function within an immune response. Some of the cellular receptors are permanently expressed on all leukocytes on a high level (MHC class I), whereas others only are expressed during certain developmental or activation stages or on certain leukocyte populations (monocytes, granulocytes, NK cells, lymphocytes) (Murphy 2012, Biosciences 2010). For different mammals (man, mouse, rat, but also swine, cattle, dog), a system of characterized leukocyte surface molecules primarily based on the recognition of these molecules by specific monoclonal antibodies (mabs) was summarized at international workshops as clusters of differentiation (CD) (Cobbold and Metcalfe 1994, Hopkins, Ross and Dutia 1993, Haverson et al. 2001, Mason et al. 2001). Using these mabs, it is not only possible to characterize the developmental and functional stage of different leukocyte subpopulations but also to define the interactions between these populations. For bony fish, such a system does not exist. Only a limited number of mabs against leukocyte surface molecules is available and most of them are strongly specific for species (Köllner et al. 2004, Köllner et al. 2001, Zhang et al. 2010, Ramirez-Gomez et al. 2012, Wen et al. 2011, DeLuca, Wilson and Warr 1983, Toda et al. 2011, Toda et al. 2009, Takizawa et al. 2011a, Hetland et al. 2010, Araki et al. 2008). The goal of this PhD work, therefore, was to develop monoclonal antibodies against surface markers of rainbow trout (Oncorhynchus mykiss) T cell population (chapter 2). The lymphocytes are characterized by the expression of a T cell receptor complex composed of TCR chains (α and β) and CD3 chains (α, β, γ, δ, ε and ζ). Cytotoxic T lymphocytes (CTLs) binds to MHC class I bound peptide on the infected host cell using their T cell receptor (TCR) and its co-receptor CD8 resulting in specific killing. Th cells recognize peptides through their T cell receptor (TCR) and their co-receptor CD4 after extracellular antigens uptake, processing and presentation via MHC class II by professional antigen presenting cells (macrophages, dendritic cells and B cells). During recent years, genes encoding MHC class I and II, TCR and their co-receptors CD8 and CD4 have been cloned in several fish species and antibodies have been developed to study protein expression in morphological and functional contexts. However, mabs specific for TCR or CD3 have not been established yet. Therefore, using pan-T cell marker specific mabs, the activation and kinetics of T cell subpopulation should be investigated (chapter 2). Moreover, a flow cytometry method was established using different lineage marker specific mabs to measure different leukocyte populations and their involvement in immune mechanisms of trout using a single tube assay (chapter 3). The first line of defense against altered body cells or pathogens is provided by evolutionarily ancient macrophages and natural killer (NK) cells. These innate mechanisms are well developed in bony fish. Two types of NK cell homologues have been described in fish: non-specific cytotoxic cells and NK-like cells (Shen et al. 2002, Shen et al. 2003, Shen et al. 2004, Fischer et al. 2013). Functional assays for innate and adaptive lymphocyte responses have been developed in only a few fish species. However, there are no tools available until now in trout to follow these cells directly in the immune response. The molecular characteristics and the expression on leukocyte subpopulations of CD56 were therefore analyzed. Furthermore, a mab that is specific for a molecule expressed only in NK cells but with uncommon expression kinetics was established (chapter 4). Overall, the established tools and methods allow a more detailed characterization of cellular immune mechanisms against intracellular pathogens in rainbow trout.
Effect of surgical intervention on the activation status of circulating monocytes and T-cells
(2009)
Major surgery causes alterations in immune function which results in immune suppression in post surgical patients. Deactivation of monocytes in these patients is characterised by the reduced ability of these cells to produce pro-inflammatory cytokines on stimulation with LPS in vitro and by markedly reduced HLA-DR expression. Immune suppression in patients with systemic inflammation has also been associated with a high level of apoptosis in both the circulating T and B cell populations. In addition post surgical T cells have a reduced capacity to proliferate ex vivo in response to co-ligation of the T cell receptor and CD-28. Considering these impairments of immune system, this study aimed to define the extent of immune modulation in both innate and adaptive system in a cohort of surgical patients. Measurment of the level of HLA-DR expression of monocytes in these patients showed a considerable change in monocyte phenotype in the immediate post operative period. In line with previous work, all patients showed a considerable reduction in monocytic surface HLA-DR expression which persisted for many hours and those who had post surgical septic complications showed the most severe reduction. Importantly, patients with minor surgical intervention also exhibited decreased HLA-DR expression. Gene expression analysis of monocyte in these patients showed the up-regulated transcripts of genes involved in extravasation and realignment of the cytoskeleton. Analysis of periperal T cell demonstrated a significant reduction in their number in the circulation and a sharp raise in the number of apoptotic T –cells in the immediate post surgical period. Microarray analysis of T cells from patients who developed sepsis and patients with an uneventful recovery within the post-operative period (3 days) showed a substantial reduction in the transcriptional activity of many genes in both groups. However, this down regulation of T cell transcriptional activity appears to be a rather broad and non specific effect since it is not restricted to particular functional pathways. Real time PCR analysis of both the CD4+ and CD8+ populations using selected down-regulated genes showed that the change in transcriptional profile is equally evident both in CD4+ and CD8+ T-cells. The cause of this transient immune depression following surgery remains to be established and it may represent an important enabling factor which contributes to the development of post surgical infections and inflammatory complications.