The overall composition of the mammalian intestinal microbiota varies between individuals: within... more The overall composition of the mammalian intestinal microbiota varies between individuals: within each individual there are differences along the length of the intestinal tract related to host nutrition, intestinal motility and secretions. Mucus is a highly regenerative protective lubricant glycoprotein sheet secreted by host intestinal goblet cells; the inner mucus layer is nearly sterile. Here we show that the outer mucus of the large intestine forms a unique microbial niche with distinct communities, including bacteria without specialized mucolytic capability. Bacterial species present in the mucus show differential proliferation and resource utilization compared with the same species in the intestinal lumen, with high recovery of bioavailable iron and consumption of epithelial-derived carbon sources according to their genome-encoded metabolic repertoire. Functional competition for existence in this intimate layer is likely to be a major determinant of microbiota composition and ...
AIMS: Infectious gastroenteritis is a recognized risk factor for subsequent development of Irrita... more AIMS: Infectious gastroenteritis is a recognized risk factor for subsequent development of Irritable Bowel Syndrome (post-infectious (PI)-IBS). Recent tragedies such as that which occurred in Walkerton, Ontario and others worldwide have highlighted some important risk factors including co-morbid anxiety and depression and female gender. However, the exact cause and effect relationship between these two conditions is unknown. Further examination of basal changes in structure and function are required to understand how the depressed gut responds to pathogenic insult, and if pre-existing clinical depression leaves patients at an increased risk for developing PI-IBS. METHODS: Olfactory bulbectomy (OBx) is a well-characterized rodent model of co-morbid anxiety and depression. OBx was performed on 8-10 week old female C57Bl/6 mice by making two burr holes in the skull overlying the olfactory bulbs. The bulbs are removed by suction, and the wound is treated with antibiotic and closed by su...
Healthy individuals live in peaceful co-existence with an immense load of intestinal bacteria. Th... more Healthy individuals live in peaceful co-existence with an immense load of intestinal bacteria. This symbiosis is advantageous for both the host and the bacteria. For the host it provides access to otherwise undigestible nutrients and colonization resistance against pathogens. In return the bacteria receive an excellent nutrient habitat. The mucosal immune adaptations to the presence of this commensal intestinal microflora are manifold. Although bacterial colonization has clear systemic consequences, such as maturation of the immune system, it is striking that the mutualistic adaptive (T and B cells) and innate immune responses are precisely compartmentalized to the mucosal immune system. Here we summarize the mechanisms of mucosal immune compartmentalization and its importance for a healthy host-microbiota mutualism.
Journal of immunology (Baltimore, Md. : 1950), Jan 15, 2014
Neutropenia is probably the strongest known predisposition to infection with otherwise harmless e... more Neutropenia is probably the strongest known predisposition to infection with otherwise harmless environmental or microbiota-derived species. Because initial swarming of neutrophils at the site of infection occurs within minutes, rather than the hours required to induce "emergency granulopoiesis," the relevance of having high numbers of these cells available at any one time is obvious. We observed that germ-free (GF) animals show delayed clearance of an apathogenic bacterium after systemic challenge. In this article, we show that the size of the bone marrow myeloid cell pool correlates strongly with the complexity of the intestinal microbiota. The effect of colonization can be recapitulated by transferring sterile heat-treated serum from colonized mice into GF wild-type mice. TLR signaling was essential for microbiota-driven myelopoiesis, as microbiota colonization or transferring serum from colonized animals had no effect in GF MyD88(-/-)TICAM1(-/-) mice. Amplification of ...
IgA is the most abundant immunoglobulin produced in mammals, and is mostly secreted across mucous... more IgA is the most abundant immunoglobulin produced in mammals, and is mostly secreted across mucous membranes. At these frontiers, which are constantly assaulted by pathogenic and commensal microbes, IgA provides part of a layered system of immune protection. In this review, we describe how IgA induction occurs through both T-dependent and T-independent mechanisms, and how IgA is generated against the prodigious load of commensal microbes after mucosal dendritic cells (DCs) have sampled a tiny fraction of the microbial consortia in the intestinal lumen. To function in this hostile environment, IgA must be induced behind the 'firewall' of the mesenteric lymph nodes to generate responses that integrate microbial stimuli, rather than the classical prime-boost effects characteristic of systemic immunity.
Mammals coexist with an extremely dense microbiota in the lower intestine. Despite the constant c... more Mammals coexist with an extremely dense microbiota in the lower intestine. Despite the constant challenge of small numbers of microbes penetrating the intestinal surface epithelium, it is very unusual for these organisms to cause disease. In this review article, we present the different mucosal firewalls that contain and allow mutualism with the intestinal microbiota.
The large production of immunoglobulin (Ig)A is energetically costly. The fact that evolution ret... more The large production of immunoglobulin (Ig)A is energetically costly. The fact that evolution retained this apparent luxury of intestinal class switch recombination to IgA within the human population strongly indicates that there must be a critical specific function of IgA for survival of the species. The function of IgA has been investigated in a series of different models that will be discussed here. While IgA has clear protective functions against toxins or in the context of intestinal viral infections, the function of IgA specific for non-pathogenic commensal bacteria remains unclear. In the context of the current literature we present a hypothesis where secretory IgA integrates as an additional layer of immune function into the continuum of intestinal CD4 T cell responses, to achieve a mutualistic relationship between the intestinal commensal microbiota and the host.
Proceedings of the National Academy of Sciences, 2007
Recent studies indicate that T cell cross-priming preferentially occurs against long-lived, stabl... more Recent studies indicate that T cell cross-priming preferentially occurs against long-lived, stable proteins. We have studied crosspriming by using the glycoprotein (GP) of lymphocytic choriomeningitis virus (LCMV), a protein that normally is not MHC class I cross-presented. This study shows that a C-terminally truncated,
ABSTRACT Thymic stromal lymphopoietin (TSLP) is constitutively expressed in the intestine and is ... more ABSTRACT Thymic stromal lymphopoietin (TSLP) is constitutively expressed in the intestine and is known to regulate inflammation in models of colitis. We show that steady-state TSLP expression requires intestinal bacteria and has an important role in limiting the expansion of colonic T helper type 17 (Th17) cells. Inappropriate expansion of the colonic Th17 cells occurred in response to an entirely benign intestinal microbiota, as determined following the colonization of germ-free C57BL/6 or TSLPR(-/-) mice with the altered Schaedler flora (ASF). TSLP-TSLPR (TSLP receptor) interactions also promoted the expansion of colonic Helios(-)Foxp3(+) regulatory T cells, necessary for the control of inappropriate Th17 responses following ASF bacterial colonization. In summary, these data reveal an important role for TSLP-TSLPR signaling in promoting steady-state mutualistic T-cell responses following intestinal bacterial colonization.Mucosal Immunology advance online publication 20 March 2013; doi:10.1038/mi.2013.12.
CD8 ؉ T cells are crucial for the control of intracellular pathogens such as viruses and some bac... more CD8 ؉ T cells are crucial for the control of intracellular pathogens such as viruses and some bacteria. Using lymphocytic choriomeningitis virus (LCMV) infection of mice-the prototypic arenavirus evolutionarily closely related to human Lassa fever and South American hemorrhagic fever viruses, we have shown previously that the kinetics of Ag presentation determine immunodominance of the LCMV-specific CTL response due to progressive exhaustion of LCMV nucleoprotein (NP)-specific CTL upon increasing viral load. In this study, we provide evidence that CTL against early LCMV NP-derived epitopes are more important in virus control than those against late glycoprotein-derived epitopes. We show that mice that are tolerant to all NP-derived T cell epitopes are severely compromised in their ability to control larger inocula of LCMV, supporting our hypothesis that CD8 ؉ T cells specific for early viral Ags play a major role in acute virus control. Thus, the kinetics with which virus-derived T cell epitopes are presented has a strong impact on the efficacy of the antiviral immunity. This aspect should be taken into consideration for the development of vaccines. The Journal of Immunology, 2008, 180: 3113-3121.
Rare cases of stable allograft acceptance after discontinuation of immunosuppression are often ac... more Rare cases of stable allograft acceptance after discontinuation of immunosuppression are often accompanied by macrochimerism (> 1% donor cells in blood) or microchimerism (< 1% donor cells in blood). Here, we have investigated whether persistence of donor cells is the cause or the consequence of long-lasting CTL unresponsiveness. We found that engraftment of splenocytes bearing a single foreign MHC class I-restricted epitope resulted in lifelong donor cell microchimerism and specific CTL unresponsiveness. This status was reversed in a strictly time-and thymus-dependent fashion when the engrafted cells were experimentally removed. The results presented herein show that microchimerism actively maintains CTL unresponsiveness toward a minor histocompatibility antigen by deleting the specific repertoire and thus excluding dominant, T cell extrinsic mechanisms of CTL unresponsiveness independent of systemically persisting donor cell antigen.
The overall composition of the mammalian intestinal microbiota varies between individuals: within... more The overall composition of the mammalian intestinal microbiota varies between individuals: within each individual there are differences along the length of the intestinal tract related to host nutrition, intestinal motility and secretions. Mucus is a highly regenerative protective lubricant glycoprotein sheet secreted by host intestinal goblet cells; the inner mucus layer is nearly sterile. Here we show that the outer mucus of the large intestine forms a unique microbial niche with distinct communities, including bacteria without specialized mucolytic capability. Bacterial species present in the mucus show differential proliferation and resource utilization compared with the same species in the intestinal lumen, with high recovery of bioavailable iron and consumption of epithelial-derived carbon sources according to their genome-encoded metabolic repertoire. Functional competition for existence in this intimate layer is likely to be a major determinant of microbiota composition and ...
AIMS: Infectious gastroenteritis is a recognized risk factor for subsequent development of Irrita... more AIMS: Infectious gastroenteritis is a recognized risk factor for subsequent development of Irritable Bowel Syndrome (post-infectious (PI)-IBS). Recent tragedies such as that which occurred in Walkerton, Ontario and others worldwide have highlighted some important risk factors including co-morbid anxiety and depression and female gender. However, the exact cause and effect relationship between these two conditions is unknown. Further examination of basal changes in structure and function are required to understand how the depressed gut responds to pathogenic insult, and if pre-existing clinical depression leaves patients at an increased risk for developing PI-IBS. METHODS: Olfactory bulbectomy (OBx) is a well-characterized rodent model of co-morbid anxiety and depression. OBx was performed on 8-10 week old female C57Bl/6 mice by making two burr holes in the skull overlying the olfactory bulbs. The bulbs are removed by suction, and the wound is treated with antibiotic and closed by su...
Healthy individuals live in peaceful co-existence with an immense load of intestinal bacteria. Th... more Healthy individuals live in peaceful co-existence with an immense load of intestinal bacteria. This symbiosis is advantageous for both the host and the bacteria. For the host it provides access to otherwise undigestible nutrients and colonization resistance against pathogens. In return the bacteria receive an excellent nutrient habitat. The mucosal immune adaptations to the presence of this commensal intestinal microflora are manifold. Although bacterial colonization has clear systemic consequences, such as maturation of the immune system, it is striking that the mutualistic adaptive (T and B cells) and innate immune responses are precisely compartmentalized to the mucosal immune system. Here we summarize the mechanisms of mucosal immune compartmentalization and its importance for a healthy host-microbiota mutualism.
Journal of immunology (Baltimore, Md. : 1950), Jan 15, 2014
Neutropenia is probably the strongest known predisposition to infection with otherwise harmless e... more Neutropenia is probably the strongest known predisposition to infection with otherwise harmless environmental or microbiota-derived species. Because initial swarming of neutrophils at the site of infection occurs within minutes, rather than the hours required to induce "emergency granulopoiesis," the relevance of having high numbers of these cells available at any one time is obvious. We observed that germ-free (GF) animals show delayed clearance of an apathogenic bacterium after systemic challenge. In this article, we show that the size of the bone marrow myeloid cell pool correlates strongly with the complexity of the intestinal microbiota. The effect of colonization can be recapitulated by transferring sterile heat-treated serum from colonized mice into GF wild-type mice. TLR signaling was essential for microbiota-driven myelopoiesis, as microbiota colonization or transferring serum from colonized animals had no effect in GF MyD88(-/-)TICAM1(-/-) mice. Amplification of ...
IgA is the most abundant immunoglobulin produced in mammals, and is mostly secreted across mucous... more IgA is the most abundant immunoglobulin produced in mammals, and is mostly secreted across mucous membranes. At these frontiers, which are constantly assaulted by pathogenic and commensal microbes, IgA provides part of a layered system of immune protection. In this review, we describe how IgA induction occurs through both T-dependent and T-independent mechanisms, and how IgA is generated against the prodigious load of commensal microbes after mucosal dendritic cells (DCs) have sampled a tiny fraction of the microbial consortia in the intestinal lumen. To function in this hostile environment, IgA must be induced behind the &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;firewall&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; of the mesenteric lymph nodes to generate responses that integrate microbial stimuli, rather than the classical prime-boost effects characteristic of systemic immunity.
Mammals coexist with an extremely dense microbiota in the lower intestine. Despite the constant c... more Mammals coexist with an extremely dense microbiota in the lower intestine. Despite the constant challenge of small numbers of microbes penetrating the intestinal surface epithelium, it is very unusual for these organisms to cause disease. In this review article, we present the different mucosal firewalls that contain and allow mutualism with the intestinal microbiota.
The large production of immunoglobulin (Ig)A is energetically costly. The fact that evolution ret... more The large production of immunoglobulin (Ig)A is energetically costly. The fact that evolution retained this apparent luxury of intestinal class switch recombination to IgA within the human population strongly indicates that there must be a critical specific function of IgA for survival of the species. The function of IgA has been investigated in a series of different models that will be discussed here. While IgA has clear protective functions against toxins or in the context of intestinal viral infections, the function of IgA specific for non-pathogenic commensal bacteria remains unclear. In the context of the current literature we present a hypothesis where secretory IgA integrates as an additional layer of immune function into the continuum of intestinal CD4 T cell responses, to achieve a mutualistic relationship between the intestinal commensal microbiota and the host.
Proceedings of the National Academy of Sciences, 2007
Recent studies indicate that T cell cross-priming preferentially occurs against long-lived, stabl... more Recent studies indicate that T cell cross-priming preferentially occurs against long-lived, stable proteins. We have studied crosspriming by using the glycoprotein (GP) of lymphocytic choriomeningitis virus (LCMV), a protein that normally is not MHC class I cross-presented. This study shows that a C-terminally truncated,
ABSTRACT Thymic stromal lymphopoietin (TSLP) is constitutively expressed in the intestine and is ... more ABSTRACT Thymic stromal lymphopoietin (TSLP) is constitutively expressed in the intestine and is known to regulate inflammation in models of colitis. We show that steady-state TSLP expression requires intestinal bacteria and has an important role in limiting the expansion of colonic T helper type 17 (Th17) cells. Inappropriate expansion of the colonic Th17 cells occurred in response to an entirely benign intestinal microbiota, as determined following the colonization of germ-free C57BL/6 or TSLPR(-/-) mice with the altered Schaedler flora (ASF). TSLP-TSLPR (TSLP receptor) interactions also promoted the expansion of colonic Helios(-)Foxp3(+) regulatory T cells, necessary for the control of inappropriate Th17 responses following ASF bacterial colonization. In summary, these data reveal an important role for TSLP-TSLPR signaling in promoting steady-state mutualistic T-cell responses following intestinal bacterial colonization.Mucosal Immunology advance online publication 20 March 2013; doi:10.1038/mi.2013.12.
CD8 ؉ T cells are crucial for the control of intracellular pathogens such as viruses and some bac... more CD8 ؉ T cells are crucial for the control of intracellular pathogens such as viruses and some bacteria. Using lymphocytic choriomeningitis virus (LCMV) infection of mice-the prototypic arenavirus evolutionarily closely related to human Lassa fever and South American hemorrhagic fever viruses, we have shown previously that the kinetics of Ag presentation determine immunodominance of the LCMV-specific CTL response due to progressive exhaustion of LCMV nucleoprotein (NP)-specific CTL upon increasing viral load. In this study, we provide evidence that CTL against early LCMV NP-derived epitopes are more important in virus control than those against late glycoprotein-derived epitopes. We show that mice that are tolerant to all NP-derived T cell epitopes are severely compromised in their ability to control larger inocula of LCMV, supporting our hypothesis that CD8 ؉ T cells specific for early viral Ags play a major role in acute virus control. Thus, the kinetics with which virus-derived T cell epitopes are presented has a strong impact on the efficacy of the antiviral immunity. This aspect should be taken into consideration for the development of vaccines. The Journal of Immunology, 2008, 180: 3113-3121.
Rare cases of stable allograft acceptance after discontinuation of immunosuppression are often ac... more Rare cases of stable allograft acceptance after discontinuation of immunosuppression are often accompanied by macrochimerism (> 1% donor cells in blood) or microchimerism (< 1% donor cells in blood). Here, we have investigated whether persistence of donor cells is the cause or the consequence of long-lasting CTL unresponsiveness. We found that engraftment of splenocytes bearing a single foreign MHC class I-restricted epitope resulted in lifelong donor cell microchimerism and specific CTL unresponsiveness. This status was reversed in a strictly time-and thymus-dependent fashion when the engrafted cells were experimentally removed. The results presented herein show that microchimerism actively maintains CTL unresponsiveness toward a minor histocompatibility antigen by deleting the specific repertoire and thus excluding dominant, T cell extrinsic mechanisms of CTL unresponsiveness independent of systemically persisting donor cell antigen.
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Papers by Markus Geuking