Homeostasis of Langerhans and Dendritic Cells in Health and Disease
Lead Research Organisation:
Newcastle University
Department Name: Institute of Cellular Medicine
Abstract
Dendritic cells are critical components of the immune system. They detect foreign material and coordinate the immune response. Without them immunity to viruses, tumours and vaccines is severely compromised. They are important in the rejection of transplanted organs and in ‘graft versus host disease‘, a complication of bone marrow transplantation. Additionally, they multiply and accumulate in ‘histiocytosis‘, a rare but potentially fatal disease.
The question we are studying is how these cells are maintained in the body. Previously they were thought to be replaced at a steady rate by cells from the blood. Recent evidence from mice suggests that they can proliferate or renew themselves but this is not known in humans. We propose to find out 1) whether human skin dendritic cells can renew themselves; 2) what controls their survival and proliferation; 3) whether they are affected by bone marrow failure. We will use normal human skin obtained from plastic surgery and small samples from patients with specific bone marrow disorders. Our experiments will help to understand how the immune system is controlled in health and disease, including bone marrow failure and transplantation. We may identify new ways to boost vaccination, prevent harmful immune responses and treat histiocytosis
The question we are studying is how these cells are maintained in the body. Previously they were thought to be replaced at a steady rate by cells from the blood. Recent evidence from mice suggests that they can proliferate or renew themselves but this is not known in humans. We propose to find out 1) whether human skin dendritic cells can renew themselves; 2) what controls their survival and proliferation; 3) whether they are affected by bone marrow failure. We will use normal human skin obtained from plastic surgery and small samples from patients with specific bone marrow disorders. Our experiments will help to understand how the immune system is controlled in health and disease, including bone marrow failure and transplantation. We may identify new ways to boost vaccination, prevent harmful immune responses and treat histiocytosis
Technical Summary
Migratory dendritic cells (DC) are key sentinels of the immune system. How they are maintained in sites of antigen exposure remains an important unresolved question in humans. Recent evidence in murine models has revised the conventional view that DC are continually replaced by bone marrow derived, blood borne precursors and suggests that some level of local self-renewal operates in the steady state. This is especially important in the case of epidermal Langerhans cells (LC). Equivalent data are lacking in humans.
Elucidating the homeostasis of human DC and LC is vital to understanding: (i) the induction of immunity or tolerance; (ii) the paradoxical preservation of adaptive immunity relative to innate defence in bone marrow failure; (iii) the tissue tropism of graft versus host disease, in which persistent proliferative recipient DC may play a key role; (iv) the accumulation of abnormal proliferating DC and LC in histiocytic disorders. Understanding the factors that promote local self-renewal may lead to new therapeutic avenues.
This project will test the hypothesis: Human Langerhans cells and other peripheral myeloid dendritic cells are maintained by local self-renewal in the steady state.
The following experimental questions will be tackled:
1. Do LC and DC synthesize DNA and proliferate in situ?
2. What controls the survival and proliferation of LC and DC ex vivo?
3. Does abnormal myelopoiesis interfere with LC and DC homeostasis?
Preliminary DNA content analysis on normal skin obtained from plastic surgery suggests that 2-3% of LC and up to 4% of dermal DC are cycling. I will further investigate this finding by testing ki-67 antigen expression, DNA synthesis (BrdU incorporation) and LC and DC stability in skin explant culture. I will then develop simple in vitro survival and DNA synthesis assays to investigate the effect of growth factors such as M-CSF, GM-CSF and flt-3L that have been identified as important to DC homeostasis in murine systems. I will also use a commercial library of kinase inhibitors as a screening tool to uncover new survival pathways for peripheral LC and DC in humans. Finally, I will use small cohorts of patients with failing or cytogenetically abnormal myelopoiesis to determine whether peripheral DC populations are depleted or contain translocations, respectively. This constitutes a unique in vivo test of the hypothesis and is directly relevant to understanding host defence in bone marrow failure syndromes.
Elucidating the homeostasis of human DC and LC is vital to understanding: (i) the induction of immunity or tolerance; (ii) the paradoxical preservation of adaptive immunity relative to innate defence in bone marrow failure; (iii) the tissue tropism of graft versus host disease, in which persistent proliferative recipient DC may play a key role; (iv) the accumulation of abnormal proliferating DC and LC in histiocytic disorders. Understanding the factors that promote local self-renewal may lead to new therapeutic avenues.
This project will test the hypothesis: Human Langerhans cells and other peripheral myeloid dendritic cells are maintained by local self-renewal in the steady state.
The following experimental questions will be tackled:
1. Do LC and DC synthesize DNA and proliferate in situ?
2. What controls the survival and proliferation of LC and DC ex vivo?
3. Does abnormal myelopoiesis interfere with LC and DC homeostasis?
Preliminary DNA content analysis on normal skin obtained from plastic surgery suggests that 2-3% of LC and up to 4% of dermal DC are cycling. I will further investigate this finding by testing ki-67 antigen expression, DNA synthesis (BrdU incorporation) and LC and DC stability in skin explant culture. I will then develop simple in vitro survival and DNA synthesis assays to investigate the effect of growth factors such as M-CSF, GM-CSF and flt-3L that have been identified as important to DC homeostasis in murine systems. I will also use a commercial library of kinase inhibitors as a screening tool to uncover new survival pathways for peripheral LC and DC in humans. Finally, I will use small cohorts of patients with failing or cytogenetically abnormal myelopoiesis to determine whether peripheral DC populations are depleted or contain translocations, respectively. This constitutes a unique in vivo test of the hypothesis and is directly relevant to understanding host defence in bone marrow failure syndromes.
