L(3)4 - Cellular Basis of Autoimmunity 2 (mainly about the rest) Flashcards
- to review the function of different leukocytes in organ-specific autoimmunity - to understand how knowledge of the cellular immunology relates to treatment strategies
What are the three signals required for full T cell activation, and what happens when they are not all present?
Signal 1: Recognition of the antigen by the T cell receptor (TCR) on the T cell, presented by an antigen-presenting cell (APC). Alone, this leads to anergy (T cell inactivation).
Signal 2: Co-stimulatory signals provided by the APC through molecules like CD80 or CD86 binding to CD28 on the T cell. Together with Signal 1, this leads to T cell activation.
Signal 3: Cytokines secreted in the microenvironment. This determines the type of immune response and provides further instruction for differentiation into specific T cell subsets (e.g., Th1, Th2).
Without all three signals, activation is incomplete, leading to energy rather than a functional immune response.
Why is co-stimulation important in T cell activation, and what is its implication in tissue culture?
It provides an additional independent pathway necessary for T cell activation. In tissue culture, presenting only the antigen (Signal 1) without co-stimulation (Signal 2) results in T cell anergy rather than activation. This demonstrates the requirement for multiple signals in a complete immune response.
What determines the cytokine environment during T cell activation, and why is this important?
the type of antigen encountered (which can be specific for the location) and the innate immune response. Different antigens elicit specific local cytokine profiles, which guide the differentiation of T cells into subsets (e.g., Th1, Th2, Th17). This is critical for tailoring the immune response to eliminate the pathogen.
What are innate lymphoid cells (ILCs), and how do they contribute to the immune response?
immune cells that lack antigen-specific receptors but play a key role in the early immune response. They produce cytokines and help shape the adaptive immune response by influencing the cytokine environment and recruiting other immune cells. Examples include ILC1, ILC2, and ILC3, which are associated with distinct immune functions.
How does molecular mimicry contribute to autoimmunity?
Molecular mimicry occurs when T cells recognise self-antigens that resemble foreign antigens (e.g., from pathogens). This can lead to the activation of autoreactive T cells, which traffic to target organs and cause local inflammation, recruiting other immune cells and resulting in tissue damage.
What happens during the activation of naive T cells that recognise autoantigens?
Naive T cells recognising autoantigens may become activated through processes like molecular mimicry or bystander activation. They then survey the body and localise to the target organ, where they encounter antigen-presenting cells expressing related antigens. This leads to local inflammation, recruitment of other immune cells (e.g., B cells), and tissue damage.
What immune cell populations are commonly found in inflamed target organs during autoimmunity?
in autoimmunity e.g. experimental autoimmune uveitis (EAU), the following immune cells are commonly found:
CD11b+Ly6G- cells: Monocytes/macrophages (largest proportion).
CD11b+Ly6G+ cells: Neutrophils.
CD4+ T cells.
Other CD45+ cells.
CD8+ T cells.
NK1.1+ cells: Natural killer cells.
What roles do regulatory cytokines like IL-10 and IL-35 play in autoimmunity?
IL-10 (anti inflammatory) and IL-35 (immunosuppressive) help mediate immune regulation and promote tolerance. They contribute to the generation of systemic and local tissue memory, facilitating periods of remission in autoimmune diseases. However, reactivation of autoimmunity can occur under certain conditions.
How can autoimmune processes in the eye (e.g., experimental autoimmune uveitis) be studied?
using induced models in mice e.g.
Taking pictures of the retina to observe damage, such as retinal thinning and colour changes, analysing immune cell populations in the retina to characterise inflammation, Identifying immune cells like CD4+ T cells, monocytes, and neutrophils that accumulate in the inflamed retina.
How do therapeutic opportunities in autoimmunity arise?
through understanding the complex interactions in the immune system e.g. targeting specific cytokines or immune pathways, modulating T cell activation and co-stimulation, addressing local tissue inflammation and repairing tissue damage and research into target organs (e.g., the eye in autoimmune uveitis) provides insights into potential treatments.
What is the significance of CD4+ T cell differentiation in human disease?
Different CD4+ T cell subsets correlate with distinct forms of human diseases. e.g. studies on leprosy revealed that resistance or susceptibility to the disease is associated with specific cytokine production patterns in CD4+ T cells.
How do cytokine patterns differ between resistant and susceptible forms of leprosy?
- Resistant form (tuberculoid leprosy): Cytokines e.g. IL-2, IFN-γ, and IL-10 correlate with strong cell-mediated immunity.
- Susceptible form (lepromatous leprosy): Multibacillary lesions with reduced resistance correlate with distinct cytokine profiles, showing weaker cell-mediated immunity.
How was the correlation between cytokine production and resistance in leprosy studied?
Skin biopsy specimens from leprosy patients were used to extract mRNA, which was amplified by PCR using cytokine-specific primers. This technique identified the cytokine profiles associated with resistant and susceptible forms of the disease.
How do transgenic T cells help study CD4+ T cell phenotypes in autoimmunity?
Transgenic T cells with TCRs that recognise specific autoantigens, e.g. MOG peptide, allow researchers to study the clinical manifestations and severity of autoimmune diseases in relation to T cell differentiation.
what is the MOG peptide
minor compnent of the CNS myelin
How do different CD4+ T cell subsets affect disease severity in autoimmunity?
correlate with varying disease severity e.g.
- Th17 cells: Produce a more severe clinical phenotype.
- Th2 cells: Produce a less severe clinical phenotype.
(highlights the link between T cell differentiation and disease outcomes)
What factors influence the differentiation of CD4+ T cells?
- Genetics plays a key role in determining effector molecules e.g. cytokines / costimulation and susceptibility.
- Costimulatory molecules influence differentiation by modulating the activation signals.
- Environmental factors e.g. how the antigen is administered (route) , its presence, activity (adjuvant), and dose
(4. dendritic cells phenotype)
How do dendritic cells influence CD4+ T cell differentiation?
in promoting the differentiation of specific T cell subsets. By presenting antigens in different contexts, dendritic cells can drive CD4+ T cells towards Th1, Th2, Th17, or regulatory T cell phenotypes.
What are the differentiation cytokines for Th1
IL-12 ( IL-18)
What are the effector cytokines for Th17
IL-6, TGFB1, IL-23 ( IL-21)
What are the effector cytokines for Treg
IL-2 and TGFB1
How is the manifestation of the T cell phenotype determined
by their transcriptio factors e.g. Th1 = Stat4, Th17 = Stat3 and Treg = FoxP3
What kind of T cells are causing organ-specific autoimmune diseases
predominantly Th1 and Th17 cells
When does T cell differentiation occur
after a naive T cell has been activated ( some phenotypes will have a much greater likelihood of causing organ specific autoimmunity and will be found in that specific organ more commonly than others)
what are Treg
regulatory T cells that play a critical role in organ specific autoimmunity
why do Treg cells play such an important role in organ-specific autoimmunity
because in a well regulated immune system, Treg cells are able to titrate the severity of inflammation in the local environment to optimise the immune response and minimise tissue damage (when they don’t work, individuals are at a greater risk of setting up a self sustaining auto immune process)
What happens if you cripple T reg cells by e.g. knocking out the FoxP3 transcription factor
you get life ending auto inflammation / immune responses to local antigens
What role do Treg cells play in autoimmunity?
they are crucial for maintaining immune homeostasis by suppressing autoreactive T cells and preventing autoimmune responses. Deficiencies in Treg numbers or function are commonly associated with autoimmune diseases, such as multiple sclerosis.
How does the local environment affect Treg function?
Treg cells rely on the cytokine IL-2 for their function. If IL-2 is limited or lost in the local environment, Treg functionality can be impaired, compromising immune regulation and increasing the risk of autoimmunity.
What happens when FoxP3 expression is lost in Treg cells?
FoxP3 is a key transcription factor required for Treg cell development and function. Loss of FoxP3 expression leads to a complete loss of Treg function, resulting in immune dysregulation and increased susceptibility to autoimmunity.
Are autoreactive cells in autoimmune environments resistant to Treg suppression?
unclear but thought that yes
This resistance might be transient, with regulation eventually kicking in and working normally.
Alternatively, the Tregs themselves might lose their suppressive ability in these environments, which remains a subject of ongoing research.
What evidence supports the resistance of effector T cells to Treg suppression in autoimmunity?
Experimental studies have shown that effector T cells from the central nervous system (CNS) or pancreas in autoimmune conditions can resist suppression by Treg cells in conventional assays, highlighting the challenges of regulating auto-inflammatory environments.
What is the role of macrophages in the immune response?
are part of the macrophage-monocyte lineage and are recruited to sites of inflammation to amplify the immune signals produced by T cells, contributing to tissue damage in autoimmune diseases.
How do macrophages differ between humans and mice?
While macrophages are functionally important in both species, there are more significant functional differences between human and mouse macrophages compared to T cells. Despite this, studying macrophages in mice provides instructive insights into their roles in immune responses and disease.
What role do macrophages play in experimental autoimmune diseases?
Studies have shown that in experimental autoimmune diseases, such as experimental autoimmune encephalomyelitis (EAE) or experimental autoimmune uveitis (EAU), depletion of macrophages prevents disease manifestation. This demonstrates that macrophages are essential for the clinical expression of autoimmune disease, even in the presence of autoreactive CD4+ T cells.
How do macrophages amplify immune signals
They interpret cytokines produced by activated C CD4+ T cells :
- In Th1 environments, macrophages produce toxic molecules like nitric oxide (NO), reactive oxygen species (ROS), tumour necrosis factor (TNF), and granulocyte-macrophage colony-stimulating factor (GM-CSF).
- In Th17 environments, macrophages respond to IL-17 and contribute to inflammation.
They also release pro-inflammatory cytokines, such as IL-6 and IL-1, which can cause tissue damage.
Do macrophages establish the type of local immune response?
There is no evidence that macrophages establish the type of T cell response (e.g., Th1, Th17), but they amplify and respond to the existing immune environment. For instance, Th1 environments can stimulate M1 macrophages, but it’s unclear if macrophages initiate the Th1 response.
How are macrophages modulated by TNF?
By two receptors :
-TNFR1: Mediates most pro-inflammatory activities of TNF.
-TNFR2: Plays other roles in immune regulation.
Blocking TNF or TNFR1 has been shown to reduce autoimmune disease severity, and TNF-targeted therapies are effective in diseases like rheumatoid arthritis.
What experiment demonstrated the importance of TNFR1 in macrophages?
In EAU studies with TNFR1 knockout mice (Ly5.1):
Macrophage recruitment was dramatically reduced in inflamed tissues.
CD4+ T cell recruitment was similar to wild-type mice.
Mice were resistant to autoimmune disease, showing that TNFR1 expression on macrophages is essential for their recruitment and the inflammatory damage in autoimmune disease.
What molecules and receptors allow macrophages to interpret the local immune environment?
via Cytokine receptors: IFNγ, IL-4/IL-13.
Toll-like receptors (TLRs): Such as TLR4.
These receptors enable macrophages to respond to Th1 or Th17 signals and amplify inflammation.
What is the purpose of the Cre-loxP system in genetic manipulation?
The Cre-loxP system allows for precise manipulation of specific genes in a cell. A gene of interest is flanked by LoxP sites, and when Cre recombinase is introduced, it removes the gene between the LoxP sites, leaving a looped-out gene and a single LoxP site.
How can gene targeting be restricted to specific cell types?
By placing Cre recombinase expression under a cell-type-specific promoter (e.g., CCR2 promoter for monocytes/macrophages), you can limit recombination to only those cells that express the promoter, thus targeting the gene in a specific cell type.
Why is the CCR2 promoter used in this experiment?
CCR2 promoter drives the expression of Cre recombinase specifically in CCR2-expressing cells, such as monocytes and macrophages, ensuring that gene manipulation (like deleting the GM-CSF receptor) occurs only in these cells.
What is the importance of GM-CSF in this study, particularly in the EAE model?
GM-CSF is a cytokine involved in immune responses. In this study, the focus is on GM-CSF receptor (Csf2rb), which is deleted in macrophages to study how these cells influence disease (EAE). GM-CSF is crucial in inflammatory responses, particularly in autoimmunity.
What is the role of Tamoxifen in this genetic model?
Tamoxifen activates Cre recombinase expression in animals with the Ccr2-creER T2+/+ construct. This allows for the conditional deletion of the GM-CSF receptor in CCR2-expressing cells only when Tamoxifen is administered, providing temporal control over gene manipulation.
What do the results from the EAE model show about GM-CSF receptor deletion?
The animals treated with Tamoxifen, where Cre recombinase is activated in CCR2-expressing cells and the GM-CSF receptor is deleted, show a significant reduction in disease (EAE). This suggests that CCR2-expressing macrophages/monocytes lacking GM-CSF receptor are resistant to disease, indicating the importance of these cells in the inflammatory process.
How does IL-1β relate to the experiment’s findings?
defect in IL-1β release from the GM-CSF receptor-deficient macrophages/monocytes contributes to the resistance to disease. This indicates that IL-1β is part of the inflammatory process driven by these cells in EAE.
What are microglia *** (question in lecture)
resident monocyte-macrophage lineage typically found in the central nervous system. Normally, they help maintain brain health, but during inflammation, they can take on a macrophage-like phenotype to respond to inflammatory signals, potentially contributing to damage in the inflamed area.
Why is it difficult to work out the origin of difference cells within the inflammatory environment *** ( question in lecture)
Because monocytes are being recruited to the site where they take on phenotypes e.g. look like microglia (not all macrophages that are responding to inflammation are necessarily blood derived monocyte macrophages)
What makes B cells efficient antigen-presenting cells (APCs)?
when presenting antigens that their B cell receptor is specific for. This specificity allows for effective antigen presentation to cognate T cells.
How do dendritic cells compare to B cells as APCs?
Dendritic cells are better at initiating immune responses as they perform extensive macropinocytosis and phagocytosis, unlike B cells, which rely on their receptor specificity for efficient antigen presentation.
What is macropinocytosis
A type of nonspecific endocytosis in which cells take up large amounts of extracellular fluid, nutrients, or soluble compounds
What is phagocytosis
a process where phagocytes engulf and destroy foreign particles
What does the experiment with TNP-specific B cells demonstrate?
That TNP-specific B cells (from TNP-LPS primed mice) have significantly higher antigen presentation efficiency compared to a non-specific B cell line (e.g., A20 cells).
Why is receptor specificity important for B cell antigen presentation?
It enables B cells to bind and present specific antigens to T cells, facilitating a robust and targeted immune response.
How can antigen-specific B cells influence autoimmune diseases?
In autoimmune diseases like autoimmune thyroid disease, antigen-specific B cells with high-affinity receptors can efficiently present self-antigens, potentially breaking tolerance and driving disease.
What is the role of haptens like TNP in immunological experiments?
to drive immune processes by mimicking antigens, helping researchers study specific immune responses.
(haptons = small molecule which, when combined with a larger carrier such as a protein, can elicit the production of antibodies which bind specifically to it)
What was the purpose of the cytochrome C immunisation experiment?
To demonstrate how tolerance can be maintained or broken when mice are immunised with human cytochrome C, mouse cytochrome C, or a mixture of both. It provides insights into mechanisms that may contribute to autoimmune diseases
What is cytochrome C
a protein found in mitochondria that helps with energy production and cell death. It’s a small, water-soluble protein with a heme group that transfers electrons.
What happens when mice are immunised with human cytochrome C?
They mount a good immune response to human cytochrome C but remain tolerant to mouse cytochrome C.
What happens when mice are immunised with mouse cytochrome C?
They remain tolerant and do not generate an immune response to either human or mouse cytochrome C, as they are tolerant to their own antigen.
What happens when mice are immunised with a mixture of human and mouse cytochrome C?
They generate an immune response to both human and mouse cytochrome C, breaking tolerance to the mouse antigen
Why does immunisation with both human and mouse cytochrome C break tolerance?
The mixture produces B cells that are cross-reactive between the two cytochromes, focusing antigen presentation of self-antigen and raising the activation threshold, allowing autoreactive T cells to become activated
What does it mean to “raise the activation threshold” and relate it back to the cytochrome C experiment
to increase the level of stimulation required to activate immune cells e.g. T cells. So when self antigens and foreign cytochrome C antigens are presented they provide a stronger and more focused signal enhancing the presentation and raising the activation threshold, so self-antigen presentation are now strong enough to overcome the tolerance mechanisms. As a result, autoreactive T cells that were previously unresponsive (tolerant) become activated and contribute to an immune response against self-antigens.
What role do B cells play in autoimmune diseases like Graves’ disease or Hashimoto’s thyroiditis?
B cells can produce pathogenic autoantibodies and expand pathogenic T cells by presenting low levels of autoantigen to cognate T cells in a focused antigen-presenting context.
What is Grave’s disease
autoimmune condition where your immune system produces antibodies that cause the thyroid to produce too much thyroid hormone
What is Hashimoto’s thyroiditis
an autoimmune disease that causes the thyroid gland to become inflamed and damaged so the thyroid no longer produces enough hormone
What was the finding in the experiment with B cell-deficient mice and EAE?
B cell-deficient mice (black blobs) could still develop experimental autoimmune encephalomyelitis (EAE), and the disease did not resolve, suggesting B cells are not strictly necessary for inducing EAE but play a role in its resolution.
What discovery was made regarding B cells and their regulatory properties?
B cells can produce regulatory cytokines like IL-10 and IL-35, which shut down T cell responses. They can also convert T cells into regulatory T cells (Tregs), highlighting their role in immune regulation.
Why are B cells considered important therapeutic targets
Because they have so many roles in the immune system e.g. regulating T cell responses, and supporting or suppressing immune activity. Targeting B cells can be crucial in managing autoimmune diseases and other immune-related conditions.
Are CD8+ T cells important in autoimmune diseases?
they are generally not considered crucial in autoimmune diseases, but evidence shows they play a critical role in the development of diabetes in NOD mice by targeting and killing islet beta cells and finding that in the draining lymph nodes stem like CD8 cells provide a reservoir of pathogenic effector cells.
What recent discovery has been made about CD8+ T cells in autoimmune disease?
Research suggests that CD8+ T cells can develop into local resident phenotypes with stem-like characteristics, providing a reservoir for ongoing pathogenicity in autoimmune conditions.
What is the role of autoreactive CD8+ T cells in NOD mice?
Autoreactive CD8+ T cells in NOD mice cause enough tissue damage to initiate an immune response, contributing to the development of spontaneous diabetes.
Why are CD4+ T cells central to autoimmune diseases?
CD4+ T cells are crucial because their recognition of autoantigens drives the disease process. However, they require antigen-presenting cells (APCs) to present these antigens, as they cannot act alone.
What are the roles of “good” and “bad” CD4+ T cells in autoimmune diseases?
“Bad” CD4+ T cells (Th1 and Th17) produce pro-inflammatory cytokines that promote disease, while “good” CD4+ T cells (Treg) regulate immune responses and help prevent excessive inflammation
Th1 and Th17 function
Th1 cells primarily function in cell-mediated immunity by producing IFNγ, activating macrophages to fight intracellular pathogens, while Th17 cells are involved in mucosal immunity, producing IL-17 which helps defend against extracellular bacteria and fungi, but can also contribute to inflammation in autoimmune diseases when dysregulated
What roles do antigen-presenting cells (APCs) play in autoimmune diseases?
APCs, such as dendritic cells and macrophages (and MDSCs) , are essential for presenting antigens to CD4+ T cells. Recruited macrophages and neutrophils can also promote ongoing disease.
What are myeloid-derived suppressor cells (MDSCs)?
MDSCs are recruited myeloid-derived cells that suppress local immune responses. In autoimmune diseases, their role is less clear, but in cancer, they can hinder immune attacks on tumours.
How do B cells and CD8+ T cells contribute to autoimmune diseases
B cells: Some promote disease by producing autoantibodies, while regulatory B cells (Bregs) may help prevent disease.
CD8+ T cells: Their role is less clear but may include promoting tissue damage or acting in specific contexts.
What is the layered or “onion” concept in autoimmune disease?
The “onion” concept illustrates the complex interplay of immune cells, with CD4+ T cells at the core, surrounded by APCs, macrophages, neutrophils, B cells, and other immune cells, all contributing to disease progression.
What is the significance of TNF as a therapeutic target in autoimmune diseases?
TNF inhibitors are effective in treating conditions like arthritis, uveitis, and Crohn’s disease. However, in multiple sclerosis, blocking TNF worsened the disease, highlighting the complexity of immune responses.
What was found in TNF knockout mice
they had less EAE, EAU and IDD
What happened in the nitic oxide knockout mice
they surprisingly developed worse autoimmunity e.g. EAE and EAU
Why was nitric oxdide experimented on as a possible therapeutic target
it is an effector molecule from macrophages known to cause tissue damage (but without disease is clinically worse)
Why did removing nitric oxide synthase or interferon-gamma worsen autoimmunity in experimental models?
These molecules help close regulatory loops in the immune process, providing negative feedback. Without them, the immune response becomes more uncontrolled, worsening the disease.
What role does IL-17 play in autoimmune diseases, and how is it targeted?
IL-17 drives inflammation and tissue damage in autoimmune diseases. Blocking IL-17 is effective in treating psoriasis, an autoimmune skin disease.
What challenges arise when targeting immune pathways in autoimmune diseases?
Immune responses often have a “yin and yang” dynamic, where blocking certain pathways may worsen the disease due to disrupting regulatory feedback loops essential for controlling inflammation.
How can targeting cell trafficking molecules help treat autoimmune diseases?
Targeting trafficking molecules can reduce immune cell movement and activity in diseases like multiple sclerosis. However, this approach often has non-specific adverse effects, such as impaired immunosurveillance, leading to complications like viral reactivation in the brain in MS.
How effective was targeting : 1. macrophages, NK cells, T cells and B cells at reducing disease
- macrophages reduce disease ( mouse)
- NK cells exacerbate disease in mouse EAE but reduce disease in mouse EAU
- T cells are effective in MS trials in both human and mouse
- B cells are effective in several different autoimmune conditions in humans and mouse
Why is targeting B cells a promising strategy for treating autoimmune diseases?
Targeting B cells, particularly using anti-CD20 therapies, has proven effective in diseases like rheumatoid arthritis, multiple sclerosis, and lupus. Newer treatments like anti-CD19 CAR T cells are being trialled for severe autoimmune conditions, showing potential but remain costly and experimental.
What is now the preferred biological treatment of choice for multiple scleoris
targeting B cells
What are anti-CD19 CAR T cells?
a type of immunotherapy used to treat certain blood cancers where a patients own immune cells are genetically modified to specifically target and destroy cells
what has Anti CD20 been NICE approved to treat
Rheumatoid arthritis in combination with methotrexate for refractory disease
What condition does Anti CD20 treatment reduce lesuin burden of
relapsing remitting multiple scleoris
(trialed in type 1 diabetes and improved beta cell survival. it has also been trialed in uvietis)
What were anti CD19 CAR T cells originally developed to target and what are they now being applied for
B cell based leukaemias but they are now being applied in serious autoimmune conditions - particularly connective tissue diseases e.g. SLE lupus and some kinds of systemic sclerosis
What challenges exist with new B cell-targeting therapies?
Current therapies like CAR T cells are expensive and experimental, requiring patient-specific engineering. Trials for off-the-shelf CAR T cells are underway, but long-term efficacy, affordability, and safety are yet to be established.
Why are B cells important in sustaining autoimmune responses?
B cells play a crucial role in sustaining long-term autoimmune responses by maintaining the immune process as cellular infiltrates evolve over time.
How has the treatment of autoimmune diseases advanced recently?
Over the past 10-15 years, there have been significant advancements, such as B cell-targeting therapies. Although progress is challenging and unpredictable, these developments offer hope for improved management of difficult autoimmune conditions.
