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Semester 6: Immunology
Immune Cells and Organs Overview of Immune System - General concepts and Haematopoeisis
Immune Cells and Organs Overview of Immune System
General Concepts of the Immune System
The immune system is a complex network of cells, tissues, and organs that work together to defend the body against harmful pathogens. It is primarily divided into two main components: the innate immune system and the adaptive immune system. The innate immune system provides immediate, non-specific defense, while the adaptive immune system targets specific pathogens and has memory capabilities.
Components of the Immune System
The immune system includes various types of immune cells such as lymphocytes (B cells and T cells), macrophages, dendritic cells, and natural killer cells. It also encompasses different organs including the bone marrow, thymus, spleen, and lymph nodes. Each component plays a crucial role in immune responses.
Haematopoiesis
Haematopoiesis is the process of blood cell formation, occurring primarily in the bone marrow. This process gives rise to various blood cells, including red blood cells, platelets, and different types of white blood cells such as lymphocytes, granulocytes, and monocytes. Understanding haematopoiesis is essential for grasping how immune cells develop and function.
Immune Response Mechanisms
The immune response comprises several mechanisms including phagocytosis, antibody production, and cell-mediated immunity. Pathogen recognition triggers an immune response involving the activation of T cells and B cells. T cells help regulate immune responses and directly kill infected cells, while B cells produce antibodies that neutralize pathogens.
Immunological Memory
One of the hallmark features of the adaptive immune system is immunological memory, which allows for a faster and more efficient response upon subsequent exposures to the same pathogen. Memory cells remain in the body long after an infection has cleared and can quickly mount an immune response to prevent re-infection.
Cells of the immune system - T and B-lymphocytes, NK cells Monocytes and macrophages Neutrophils, eosinophils, and basophils -Mast cells and dendritic cells
Cells of the immune system
T-lymphocytes
T-lymphocytes, or T cells, are a type of white blood cell that play a central role in cell-mediated immunity. They are derived from the thymus and are essential for the adaptive immune response. There are several types of T cells, including helper T cells, cytotoxic T cells, and regulatory T cells. Helper T cells assist other immune cells, cytotoxic T cells kill infected or cancerous cells, and regulatory T cells help maintain immune tolerance.
B-lymphocytes
B-lymphocytes, or B cells, are responsible for humoral immunity. They develop in the bone marrow and produce antibodies against antigens. When activated by a specific antigen, B cells differentiate into plasma cells, which secrete antibodies. Memory B cells are also formed, providing long-term immunity against previously encountered pathogens.
Natural Killer Cells
Natural Killer (NK) cells are a type of lymphocyte that play a crucial role in the innate immune response. They are involved in the direct killing of virus-infected cells and tumor cells. NK cells can recognize stressed cells in the absence of antibodies, allowing for a rapid immune response.
Monocytes and Macrophages
Monocytes are a type of white blood cell that circulate in the bloodstream and can differentiate into macrophages and dendritic cells once they migrate into tissues. Macrophages are large phagocytic cells that engulf and digest cellular debris, foreign substances, and pathogens. They play a vital role in both innate and adaptive immunity.
Neutrophils, Eosinophils, and Basophils
Neutrophils are the most abundant type of white blood cell and are the first responders to infection. They engulf and destroy pathogens through phagocytosis. Eosinophils are primarily involved in combating parasitic infections and mediating allergic responses. Basophils play a role in inflammatory responses and release histamine and other chemicals involved in allergy and asthma.
Mast Cells
Mast cells are found in tissues and play a key role in allergic reactions and defense against parasites. They release histamine and other mediators during immune responses, leading to inflammation and other symptoms associated with allergies.
Dendritic Cells
Dendritic cells are antigen-presenting cells that capture and process antigens, presenting them to T cells. They act as a bridge between the innate and adaptive immune systems, initiating the adaptive immune response when they encounter pathogens.
Organs of the Immune system Primary lymphoid organs - Thymus and bone marrow
Organs of the Immune System - Primary Lymphoid Organs - Thymus and Bone Marrow
Introduction to Primary Lymphoid Organs
Primary lymphoid organs are crucial for the development and maturation of immune cells. They provide the necessary environment for lymphocyte generation.
Bone Marrow
Bone marrow is the first organ where hematopoiesis occurs, generating various blood cells including lymphocytes. It is the primary site of B cell maturation. The microenvironment in bone marrow supports the proliferation and maturation of stem cells.
Thymus
The thymus is responsible for the maturation of T lymphocytes. Located in the upper chest, the thymus provides a unique microenvironment for T cell development, including selection processes that ensure self-tolerance.
Functions of Thymus and Bone Marrow
Bone marrow produces immature lymphocytes which migrate to the thymus to mature into functional T lymphocytes. Both organs work in conjunction to ensure a balanced immune response.
Clinical Significance
Understanding the functions of thymus and bone marrow has great implications in immunology, particularly in diseases such as leukemia and immunodeficiency disorders.
Secondary Lymphoid organs - Lymph nodes and spleen Lymphatic tissues - Peyers patches and Kupffer cells, MALT, GALT and CALT
Secondary Lymphoid Organs
Lymph Nodes
Lymph nodes are small, bean-shaped structures scattered throughout the lymphatic system. They play a crucial role in the immune system by filtering lymph fluid and housing lymphocytes, such as B cells and T cells, that respond to pathogens. Each lymph node contains specialized regions, including the cortex and medulla, which facilitate the interaction of immune cells.
Spleen
The spleen is the largest secondary lymphoid organ located in the upper left abdomen. It functions to filter blood, recycle iron from red blood cells, and mount immune responses against blood-borne pathogens. The spleen contains white pulp for immune responses and red pulp for filtering and removing aged or damaged red blood cells.
Peyer's Patches
Peyer's patches are specialized lymphoid tissues located in the intestines, primarily in the ileum. They play an essential role in monitoring intestinal bacteria and generating immune responses to pathogens. Peyer's patches contain clusters of lymphoid follicles and are integral to gut-associated lymphoid tissue.
Kupffer Cells
Kupffer cells are specialized macrophages located in the liver. They play a significant role in the immune response by phagocytosing pathogens and dead cells, as well as producing various cytokines to modulate the immune response. Kupffer cells are crucial in maintaining immune tolerance to gut-derived antigens.
MALT (Mucosa-Associated Lymphoid Tissue)
MALT refers to lymphoid tissues located in mucosal areas, including the respiratory and gastrointestinal tracts. It encompasses structures like tonsils and Peyer's patches and is integral for initiating immune responses at mucosal surfaces.
GALT (Gut-Associated Lymphoid Tissue)
GALT is a component of MALT, specifically focusing on the gut. It includes Peyer's patches and isolated lymphoid follicles, which function to protect against gut pathogens and maintain tolerance to non-harmful antigens.
CALT (Cutaneous-Associated Lymphoid Tissue)
CALT comprises lymphoid tissues present in the skin, including lymphocytes and antigen-presenting cells. This system plays a critical role in immune surveillance and responses to skin pathogens and allergens.
Innate and Adaptive Immunity Anatomical barriers, Inflammatory response, Cells and molecules involved in innate immunity, Adaptive immunity Cell mediated and humoral
Innate and Adaptive Immunity
Anatomical Barriers
Anatomical barriers serve as the first line of defense against pathogens. These include the skin, mucous membranes, and other physical barriers that prevent the entry of microorganisms into the body. Skin acts as a protective shield, while mucous membranes trap pathogens in various body openings.
Inflammatory Response
The inflammatory response is a key component of innate immunity. It is initiated when tissue is damaged or infected. Signs of inflammation include redness, heat, swelling, and pain. This response involves increased blood flow, the release of signaling molecules, and attraction of immune cells to the site of injury or infection.
Cells Involved in Innate Immunity
Innate immunity involves various cell types, including macrophages, neutrophils, dendritic cells, natural killer cells, and mast cells. These cells recognize and respond to pathogens rapidly. Macrophages and neutrophils engulf and destroy pathogens, while dendritic cells present antigens to adaptive immune cells.
Molecules Involved in Innate Immunity
Key molecules in innate immunity include cytokines, chemokines, and complement proteins. Cytokines are signaling proteins that mediate and regulate immunity, inflammation, and hematopoiesis. The complement system consists of proteins that enhance the ability of antibodies and phagocytic cells to clear pathogens.
Adaptive Immunity Overview
Adaptive immunity is characterized by specificity and memory. It is activated when innate immune responses are insufficient. This system involves lymphocytes, specifically B cells and T cells, which recognize specific antigens.
Cell-Mediated Immunity
Cell-mediated immunity is primarily carried out by T cells. Helper T cells assist in activating B cells and cytotoxic T cells target and destroy infected cells. This pathway is crucial for fighting intracellular pathogens.
Humoral Immunity
Humoral immunity involves the production of antibodies by B cells. When B cells encounter a pathogen, they differentiate into plasma cells, which secrete antibodies specific to that pathogen. Antibodies neutralize pathogens and facilitate their clearance.
Receptors and Signaling Cytokines and Chemokines - General Properties of Cytokines and Chemokines
Receptors and Signaling Cytokines and Chemokines - General Properties of Cytokines and Chemokines
Introduction to Cytokines and Chemokines
Cytokines are small signaling proteins that mediate and regulate immunity, inflammation, and hematopoiesis. Chemokines are a subset of cytokines that specifically attract immune cells to sites of infection or inflammation.
Types of Cytokines
Cytokines can be classified into different types including interleukins (IL), tumor necrosis factors (TNF), growth factors, and interferons (IFN). Each type has specific functions and roles in immune responses.
Properties of Cytokines
Cytokines exhibit several general properties including pleiotropy (ability to act on multiple cell types), redundancy (multiple cytokines can have similar effects), synergy (combined action of cytokines enhances effect), and antagonism (some cytokines can inhibit the action of others).
Chemokine Functions
Chemokines primarily function to guide the migration of leukocytes during immune responses. They play essential roles in processes such as leukocyte recruitment, organ development, and angiogenesis.
Cytokine Receptors
Cytokines exert their effects by binding to specific receptors on target cells. These receptors are often associated with signal transduction pathways that lead to changes in gene expression and cellular responses.
Signaling Pathways Mediated by Cytokines
Upon cytokine binding, various signaling pathways are activated, including JAK-STAT, MAPK, and NF-kB pathways. These pathways lead to cellular activation, proliferation, and differentiation.
Clinical Relevance of Cytokines and Chemokines
Dysregulation of cytokine and chemokine signaling is implicated in various diseases, including autoimmune disorders, cancer, and infectious diseases. Therapeutics targeting these pathways are under investigation for various conditions.
Major Histocompatibility Complex MHC Organization and inheritance of the MHC
Major Histocompatibility Complex Organization and Inheritance
Introduction to MHC
The Major Histocompatibility Complex is a critical component of the immune system. It is responsible for the presentation of peptides derived from pathogens to T cells, thus playing a pivotal role in adaptive immunity.
MHC Class I and Class II
MHC molecules are classified into two main classes: Class I and Class II. MHC Class I molecules present peptides to CD8+ cytotoxic T cells, while Class II molecules present to CD4+ helper T cells.
MHC Gene Organization
The MHC genes are located on chromosome 6 in humans and are closely packed. They include several loci, including HLA-A, HLA-B, HLA-C (Class I) and HLA-DP, HLA-DQ, HLA-DR (Class II).
Polymorphism and Diversity of MHC
The MHC is highly polymorphic, with many different alleles present in the population. This diversity is crucial for the immune system's ability to recognize a wide range of pathogens.
Inheritance of MHC
MHC genes are inherited in a codominant manner, meaning that both maternal and paternal alleles are expressed. This results in a unique MHC profile for each individual.
MHC and Transplantation
MHC compatibility is a key factor in organ transplantation. Mismatched MHC can lead to graft rejection due to the immune response against foreign MHC molecules.
Clinical Relevance of MHC
Understanding MHC is important in various fields such as immunology, transplantation, and vaccine development. MHC typing is routinely performed to assess compatibility for organ transplants.
Structure and cellular distributionof HLA antigens
Introduction to HLA Antigens
HLA antigens, or Human Leukocyte Antigens, are proteins found on the surface of white blood cells and other tissues in the body. They play a crucial role in the immune system by presenting foreign molecules to T cells, thereby triggering an immune response.
Structure of HLA Antigens
HLA molecules are categorized into two main classes: Class I and Class II. Class I HLA antigens are expressed on nearly all nucleated cells and present endogenous peptides. Class II HLA antigens are primarily expressed on antigen-presenting cells, such as B cells and macrophages, and present exogenous peptides.
Cellular Distribution of HLA Antigens
HLA Class I molecules are widely distributed across tissues, with high expression in lymphoid tissues, while Class II molecules are more restricted, being primarily found in professional antigen-presenting cells. This distribution is critical for their function in immune surveillance and response.
HLA Antigens and Disease
Variations in HLA antigen distribution and expression can be associated with various diseases, particularly autoimmune disorders and transplant rejection. The understanding of HLA compatibility is vital in organ transplantation to reduce the risk of graft-versus-host disease.
Conclusion
The structure and cellular distribution of HLA antigens are fundamental to their role in the immune system. Continued research in this area holds promise for advancements in immunology, transplantation, and the treatment of autoimmune diseases.
Antigen and Antibodies Antigens- Antigenicity
Antigen and Antibodies
Definition of Antigens
Antigens are substances that can induce an immune response in the body. They are typically foreign molecules such as proteins, polysaccharides, or nucleic acids.
Types of Antigens
Antigens can be classified into two main types: exogenous antigens, which originate from outside the body, and endogenous antigens, which are produced within the body, often as a result of a viral infection.
Antigenicity
Antigenicity refers to the ability of a substance to evoke an immune response. Not all antigens are equally immunogenic, and factors such as molecular size, complexity, and stability influence their antigenicity.
Antibodies
Antibodies, or immunoglobulins, are proteins produced by B cells in response to antigens. They specifically bind to antigens and help neutralize or destroy them.
Mechanism of Antibody Action
Antibodies can neutralize pathogens, opsonize them for easier phagocytosis, or activate the complement system, leading to the destruction of the pathogen.
Applications of Antigens and Antibodies
Antigens and antibodies are widely used in diagnostic tests, vaccines, and therapeutic treatments. Their specificity is utilized in various immunological assays.
