Lymphatics and the Immune System

Lymphatic System The lymphatic system actually consists of two semi-independent systems Lymphatic Capillaries and Vessels Lymphoid Tissues and Organs

Lymphatic System One way system: to the heart Return of collected excess tissue fluid Return of leaked protein “Lymph” is this fluid Edema results if system blocked or surgically removed

Lymph capillaries Have one way minivalves allowing excess fluid to enter but not leave Picks up bacteria and viruses as well as proteins, electrolytes and fluid (lymph nodes destroy most pathogens)

Lymph flows from the lymphatic capillaries through successively larger and thicker vessels. Capillaries – Collecting Vessels – trunks – lymph ducts. With in this net work of tubing are Lymph Nodes. Lymph is transported by the same mechanism that moves blood back to the heart. - squeezing of skeletal muscles - pressure changes in the bodies cavities - capillary action and valves to prevent back flow

Lymph Nodes * * Superficial groups -Cervical -Axillary -Inguinal Deep groups -Tracheobronchial -Aortic -Iliac *

Lymph nodes: bean shaped organs along lymphatic collecting vessels. Two basic functions: Filters: Macrophages remove and destroy microorganisms and debris. Immune activation: Lymphocytes monitor the lymph for invaders.

Surrounded by a fibrous capsule Connective tissue strands called trabeculae divide up the node into compartments. There are three distinct regions histologically Cortex Medullary Cords Lymph Sinuses

Lymph node anatomy The cortex contains densely packed follicles that produce B-cells (a type of lymphocyte). T-cells (another type of Lymphocyte) can also be stored in the cortex.

Lymph Node The Medullary Cords are thin projections from the cortex deeper into the node. The cords can hold the lymphocytes, but also plasma cells.

Lymph Nodes The lymph sinuses are large reticular fibers that span the node. They contain the macrophages that consume debris and invaders.

Lymphoid Organs Lymphoid organs Lymph nodes Spleen Thymus Tonsils Small intestine & appendix aggregated lymphoid nodules

Spleen The spleen provides a site for lymphocyte proliferation. It also extracts damaged and aged blood cells. Produces erythrocytes in a fetus. Stores blood platelets

Thymus The thymus releases the hormones thymosin and thymopoietin. These hormones cause T-cells to full develop their their ability to kill certain pathogens.

Tonsils Tonsils have a variety of locations in and near the pharynx. The oral tonsils are the most likely to get infected. All tonsils house lymph follicles that produce lymphocytes and filter lymph.

Intestines and Appendix Peyer’s Patches are large clusters of lymph tissue on the intestines. There are also similar patches in the appendix. They destroy bacteria and generate “memory lymphocytes” for immunity.

Components of the immune system Innate immune system Response is non-specific Exposure leads to immediate maximal response Cell-mediated and humoral components No immunological memory Found in nearly all forms of life (plants & animals) Adaptive immune system Pathogen and antigen specific response Lag time between exposure and maximal response Cell-mediated and humoral components Exposure leads to immunologic memory Found only in jawed vertebrates

External Innate Defenses The skin secretions we produce are acidic helping to fight fungus and bacteria. Mucus comes from a variety of membranes and is meant to trap and filter incoming particles. Salivia cleans and prtotects our oral cavity. Eyes produce lacrimnal fluid that contains lysozyme a natural bacteria killer.

Internal Innate Defenses When we get hurt or infected with a virus, bacteria or fungi the body activates the inflammatory response. The symptoms of the response are: Swelling Redness Heat Pain

Internal Innate Defenses Steps of Infalmmatory Rsponse Step 1: A flood of inflammatory chemical are released into the tissue. Step 2: Epithelial cells and Macro phages release cytokines that promote inflammation and attract WBC’s

Internal Innate Defenses Step 2 continued: At the same time other cells (phagocytes, lymphocytes, etc.) release other chemicals (histamine, kinins, prostagladins and complement). All of these chemical have different roles in inflammation, but they all cause more blood flow to the area and capillaries release clotting factors and antibodies.

Internal Innate Defenses Step 3: The major players (lymphocytes, antibodies, etc) of the adaptive immune system are activated.

Internal Innate Defenses Phagocytes: The main phagocyte is the macrophage (big eater). They wonder through tissue looking for debris and invaders to phagocytize (eat).

Internal Innate Defenses Neutrophils: WBC that phagocitize infectious material Eosinophils: WBC that phagocitize parasites. Mast Cells: WBC that phagoitize bacteria.

Internal Innate Defenses Natural Killer cells: a unique group of defensive cells that patrol the blood and lymph killing cancer cells and viruses. Not phagocytic. They release chemicals called perforins that break down the cells membranes and disintegrate the nucleus.

Internal Innate Defenses Antimicrobial Proteins attack microorganisms directly or keep them from reproducing: Two most important antimicrobials Interferon Complement

Internal Innate Defenses Infected cells produce small proteins called Interferons. The interferons diffuse to healthy cells and synthesize a protein that interferes with the viruses ability to replicate.

Internal Innate Defenses Complement is actually short for Complement System. It is a group of over 20 plasma proteins that circulate in the blood. Normally inactive, when inflammation response is stimulated these chemicals enhance every aspect of the response.

Internal Innate Defenses Fevers are another form of natural defense. A mild fever causes the body stores zinc and iron instead of producing them. Bacteria require large amounts of both. It also speeds up the metabolic rate, which speeds up tissue repair.

Components of the immune system Innate immune system Response is non-specific Exposure leads to immediate maximal response Cell-mediated and humoral components No immunological memory Found in nearly all forms of life (plants & animals) Adaptive immune system Pathogen and antigen specific response Lag time between exposure and maximal response Cell-mediated and humoral components Exposure leads to immunologic memory Found only in jawed vertebrates

Adaptive Immunity The adaptive immune response is more complex than the innate. The antigen first must be recognized. The three crucial cell types include: Antigen – presenting cells B Cells T Cells

Antigens Antigens are anything that can provoke an immune response. There are two types of antigens Complete: ability to stimulate proliferation of and react with specific lymphocytes and antibodies. Incomplete: small molecules that have hooked up with the bodies own proteins and the immune system does not recognize them.

“Humoral” vs “Cell mediated” Antibody-mediated (humoral) immunity – attack by circulating antibodies released by the plasma cells derived from activated B cells. This response is only good for non complicated “obvious” bacteria or invaders. Cell-mediated immunity - direct attack by activated T cells (react with foreign antigens on the surface of other host cells). This response deals with more complicated or unknown invaders. These two systems interact with each other

Antigen-Presenting Cells APC’s engulf anitgens and display fragments of the antigen on their cell membrane for identification by T-cells or B-cells.

B Cells (humoral response) The B-cell with the correct receptor complex is duplicated many times. Called Colonial Selection. Differentiate into plasmocytes (plasma cells) when stimulated by exposure to an antigen. Most of the clones produce antibodies that kill the antigen .

B -Cells Memory B cells: produced by activated B cells that do not turn into plasma cells. Upon re-exposure the memory B cells go into immediate action and your body is able to handle the invader faster, more efficiently and actually produces way more of the correct B-cells.

Passive and Active Humoral Immunity Active Immunity: The proliferation of B-cells and their production of antibodies by your own body. Passive Immunity: When those antibodies and B-cells are acquired from an outside source. A fetus has the same immunity as his/her mother for the first few days after birth.

Cell mediated response What the B-cells miss or are not programmed to deal with T-cells are able to handle. Usually

T Cells 80% of circulating lymphocytes. Much more complex structure. All T cells get “primed” to fight a certain antigen in the Thymus gland. Some of the types: Regulatory T cells Cytotoxic T cells Memory Cells Suppressor T cells

T Cell response How T-cells respond is similar to B-cells. They identify the antigen The correct T-cell goes through colonial selection and proliferation. Then the correct T-cell performs it’s specific function (phaocytosis, chemical secretion, or signaling other cells)

Regulator T-Cells Once regulatory (helper) T-cells have bound with an antigen they stimulate proliferation of B cells and other Tcells. Without helper T-cells your body would not know to send out the killer Tcells nor what antigen to fight.

Cytotoxic T cells Cytotoxic (killer) T cells: attack foreign cells or body cells infected by viruses (“cell-mediated immunity”). They roam freely around the body looking for infected cells to chemically Kill. They can be called to action in a certain area by helper T-cells.

Memory Cell Memory T cells: produced by the division of activated T cells following exposure to a particular antigen (remain on reserve, to be reactivated following Basically they remember the shape of a certain antigen and upon coming in contact know exactly which immune cell to call.

Suppressor T Cells Also a type of regulator cell, but this one releases the chemical signal that stops the production of B and T cells.

Development of lymphocytes Originate in bone marrow from lymphoid stem cells B cells stay in bone marrow, hence “B” cells T cells mature in thymus, hence “T” cells These divide rapidly into families Each has surface receptors able to recognize one unique type of antigen= immunocompetence

The immune system protects organisms with layered defenses of increasing specificity Most simply, 1. physical barriers prevent pathogens such as bacteria and viruses from entering the body If a pathogen breaches these barriers, the 2. innate immune system provides an immediate, but non-specific response Innate immune systems are found in all plants and animals If pathogens successfully evade the innate response, vertebrates possess a third layer of protection, the 3. adaptive immune system Here, the immune system adapts its response during an infection to improve its recognition of the pathogen This improved response is then retained after the pathogen has been eliminated, in the form of an immunological memory, and allows the adaptive immune system to mount faster and stronger attacks each time this pathogen is encountered