Anatomía Funcional del Sistema Inmune: Hematopoyesis, Órganos linfoides, Sistema Linfático.

Anatomy and Function of the Immune System

Introduction to the Immune System

• The video introduces the topic of functional anatomy of the immune system, emphasizing its educational purpose.

• The content outline includes anatomical division, immune cells, hematopoiesis, lymphoid organs, and the lymphatic system.

Anatomical Division of the Immune System

• The immune system is categorized into three main components: cells, lymphoid organs, and transport systems.

• All blood cells, including immune cells, originate from hematopoietic stem cells (HSC), which differentiate into myeloid and lymphoid lineages.

Immune Cell Types

• Myeloid lineage produces granulocytes (basophils, neutrophils, eosinophils), monocytes (which can become macrophages and dendritic cells).

• Lymphoid lineage includes natural killer (NK) cells, B lymphocytes (which differentiate into plasma cells producing antibodies), and T lymphocytes with various subpopulations like CD4+ helper T-cells and CD8+ cytotoxic T-cells.

Lymphoid Organs

• Primary lymphoid organs are bone marrow and thymus; secondary organs include spleen and lymph nodes.

• Mucosal-associated lymphoid tissue (MALT) varies by location in the body: gut-associated (GALT), bronchus-associated (BALT), skin-associated (SALT), urinary tract-associated.

Hematopoiesis Process

• Hematopoiesis refers to blood cell formation from HSC in bone marrow.

• Stem cells have regenerative capacity and differentiation potential; classifications include totipotent (e.g., zygote), pluripotent (germ layers), multipotent (single tissue type).

Differentiation of Blood Cells

• HSC differentiates into myeloid or lymphoid lineages during hematopoiesis.

• Myeloid lineage yields white blood cells like neutrophils and red blood cells like erythrocytes; linfoide lineage produces B/T lymphocytes.

Summary of Immunity Types

Hematopoiesis and Myeloid Lineage Overview

Key Genes in Hematopoiesis

• The gene catados is crucial for the development of all hematopoietic lineages, providing self-renewal capabilities.

• Ikaros plays a significant role in lymphoid development.

• The noche gene is important for the differentiation between T and B lymphocyte lines.

Myeloid Lineage Cells

• The myeloid lineage consists of two main cell types: granulocytes and antigen-presenting cells.

• Granulocytes include neutrophils, basophils, mast cells, and eosinophils; they contain granules with various proteins that perform functions such as direct pathogen damage and tissue remodeling.

Neutrophils

• Neutrophils account for 50-70% of total leukocytes, with normal blood values ranging from 4,400 to 7,700 per milliliter.

• Their granules contain proteins like collagenase for tissue remodeling and antimicrobial peptides (e.g., defensins).

• They are the first responders to injury sites, engaging in phagocytosis and releasing granule contents to combat pathogens.

Basophils

• Comprising 1-3% of total leukocytes, basophils have blood concentrations ranging from 40 to 200 cells per milliliter.

• Their granules contain cytokines (e.g., IL-4), lipid mediators (e.g., leukotrienes), and histamine which modulate adaptive immune responses but are not phagocytic.

Mast Cells

• Representing less than 1% of leukocytes, mast cells are not found in circulation but play a key role in allergic responses similar to basophils.

Eosinophils

• Also less than 1% of total leukocytes with normal counts around 200 cells per milliliter; their granules contain cationic proteins that induce reactive oxygen species formation.

• Eosinophils participate in phagocytosis and are particularly involved in defense against parasites while also contributing to allergy symptoms.

Antigen-Presenting Cells (APCs)

• APCs ingest pathogens, digest their proteins into peptides, and present them on their surface to naïve lymphocytes.

Monocytes

• Normal monocyte levels range from 300 with a variation from 0 to 800; they constitute about 5–10% of total leukocytes.

Macrophages

• Derived from monocytes within tissues; they engage in phagocytosis, antigen presentation, tissue repair, and can adapt based on their location (e.g., osteoclasts in bone).

Dendritic Cells

Immune System Cells and Their Functions

Phagocytosis and Antigen Presentation

• Three forms of phagocytosis are mentioned: Mendocinos, receptor-mediated, and pinocytosis (the latter being the endocytosis of liquid). After processing antigens, these cells migrate to lymph nodes for antigen presentation to naive T lymphocytes.

Dendritic Cells and Lymphocyte Selection

• Plasmacytoid dendritic cells play a crucial role in recognizing viral nucleic acids. Follicular dendritic cells, although not produced in bone marrow, are vital for B lymphocyte selection in the spleen and lymph nodes.

Lymphoid Lineage Identification Challenges

• Identifying lymphoid lineage cells is challenging due to morphological similarities; differentiation relies on surface protein expression. A nomenclature system using "CD" (cluster of differentiation) has been established for identification.

B Lymphocytes and Their Development

• Each B lymphocyte expresses a specific antigen receptor (BCR). They mature in the bone marrow with two subpopulations: B1 cells and marginal zone B cells, which develop independently of T-cells. Follicular B cells depend on T-cell interaction for high-affinity antibody production.

T Lymphocytes: Types and Functions

• T lymphocytes express T-cell receptors (TCR) and mature in the thymus. CD4+ helper T-cells assist in various immune functions including B cell differentiation, while CD8+ cytotoxic T-cells target infected cells for destruction. Regulatory T-cells suppress immune responses to prevent damage to host tissues.

Natural Killer Cells Mechanism

• Natural killer (NK) cells express non-specific receptors that recognize MHC class I molecules present on all nucleated body cells. When encountering abnormal or tumor cells lacking MHC class I, NK cells become activated to induce cell lysis through cytotoxicity.

Primary Lymphoid Organs

Bone Marrow Functionality

• The primary function of bone marrow is generating and maturing immune system cells from hematopoietic stem cells. Active hematopoiesis occurs primarily in bones like the femur, ilium, and sternum.

Thymus Role in Immune Development

T-Cell Development in the Thymus

Immature T-Lymphocytes and Their Migration

• Immature T-lymphocytes enter the thymus at the cortico-medullary junction, where they are classified as double negative (DN) because they lack both CD4 and CD8 markers.

Proliferation and Positive Selection

• These double-negative lymphocytes migrate to the subcapsular cortex, proliferate, and express a unique T-cell receptor (TCR), transitioning into double-positive (DP) cells that express both CD4 and CD8 markers.

Interaction with Antigen-Presenting Cells

• The positive selection process involves selecting lymphocytes capable of interacting with major histocompatibility complex (MHC) molecules presented by stromal cells, essential for recognizing antigens in the body.

Intensity of Response and Apoptosis

• Lymphocytes must not only recognize antigens but also respond appropriately; those with excessive reactions undergo apoptosis to prevent potential harm to the organism.

Final Maturation of T-Lymphocytes

• Mature thymic lymphocytes transition from being double-positive to single-positive, expressing either CD4 or CD8 exclusively before entering circulation.

Secondary Lymphoid Organs: Functions and Structures

Role of Secondary Lymphoid Organs

• Secondary lymphoid organs present antigens through dendritic cells, differentiating naïve B and T lymphocytes into various populations crucial for immune response.

Structure of Lymph Nodes

• Lymph nodes develop organized microenvironments called lymphoid follicles for B cell development. Key areas include:

• Cortex: Contains macrophages and dendritic cells.

• Paracortex: Hosts T lymphocytes and dendritic cells.

• Medulla: Where mature lymphocytes exit into efferent lymphatic circulation.

Antigen Transport Mechanism

• Antigens travel from infected tissues to the cortex via afferent lymphatics. Naïve lymphocytes enter through specialized high endothelial venules to interact with presented antigens.

Activation Pathways for B-Lymphocytes

Activation Requirements for B-Lymphocytes

• Naïve B-cells require two signals for activation:

• Binding to an antigen via their B-cell receptor (BCR).

• Direct contact with activated CD4+ T-cells.

Differentiation Outcomes Post Activation

• Upon successful activation, B-cells can differentiate into plasma cells producing antibodies or return to establish germinal centers within secondary follicles, forming secondary follicles upon germinal center establishment.

The Spleen's Role in Immune Response

Functionality of the Spleen

• The spleen filters blood, capturing circulating antigens. It plays a significant role in systemic infections due to its structural organization:

• Red Pulp: Contains macrophages and erythrocytes; involved in hemolysis.

• White Pulp: Composed of periarteriolar lympoid sheaths (PALS), facilitating immune responses through germinal center formation.

Overview of the Immune System and Lymphatic Functions

Key Components of the Immune Response

• The spleen is populated with macrophages and B lymphocytes, serving as the first line of defense against blood antigens.

• Additional functions of the spleen include iron metabolism, thrombus storage, and hematopoiesis.

Mucosal Associated Lymphoid Tissue (MALT)

• MALT is identified as a secondary lymphoid organ containing T and B lymphocytes located in mucous membranes across various organs such as the digestive, respiratory, and urogenital systems.

• The gut-associated lymphoid tissue (GALT), which includes both loose clusters of lymphocytes and more structured formations like Peyer's patches in the intestines, plays a crucial role in immune response.

Structures Supporting Immune Function

• Various structures within MALT assist in immune responses; notable examples include M cells and intraepithelial lymphocytes that present antigens.

• Immunoglobulin A (IgA) is highlighted as a key immunoglobulin involved in mucosal defense mechanisms.

Skin-associated Lymphoid Tissue

• Skin-associated tissues contain elements like Langerhans cells that act as antigen-presenting cells. Other tissues mentioned include those associated with the gastrointestinal tract and genitourinary system.

The Lymphatic System's Role

• The lymphatic system comprises vessels responsible for transporting immune cells alongside the circulatory system; it contains protein-rich fluid called lymph derived from blood plasma.

• Two main lymphatic ducts are described: the thoracic duct (left duct), which collects lymph from most body parts except specific regions on the right side, draining into subclavian veins.

Drainage Mechanisms of Lymphatic Ducts