Lymphatic System and Immunity

BIO 232

Anatomy and Physiology II

Lymphatic System

• 1. Transports interstitial (tissue) fluid initially formed as blood filtrate back to the blood

• 2. Transports absorbed fat from small intestine to blood

• 3. Cells of lymphatic system - lymphocytes - fight disease

Structure of Lymphatic Vessels

• Lymph capillaries

• Closed end tubes - vast network

• Tissue fluid - called lymph

• Lymph vessels

• Similar to veins in structure

• Empty into

• Thoracic duct - to Lt subclavian vein

• Right lymphatic duct - Rt subclavian vein

Lymph capillaries

Structure of Lymphatic Vessels

• Lymph vessels

• Lymph nodes - filter lymph

• Lymphoid organs

• e.g.. Thymus, tonsils & spleen

Anatomy of the Lymphatic System

Structure of a Lymph Node

Immune System

Innate (Nonspecific) Defenses

• Barriers to Entry

• Skin & mucous membranes

• Oil gland - secretion kills bacteria

• Respiratory lining

• pH of the stomach

• Normal bacteria in the gut & vagina

• Prevents pathogens from taking up residence

Innate (Nonspecific) Defenses

• Phagocytosis

• Neutrophils - first on the scene

• Monocytes - (macrophages)

• Organ specific phagocytes

• Liver, spleen, lymph nodes, lungs & brain

• Kuphler cells - liver - fixed phagocytes

Phagocyte Mobilization

Innate (Nonspecific) Defenses

• Fever

• Hypothalamus - thermoregulatory center

• Set point is body temp - 37°C

• Fever occurs because an endogenous pyrogen (from lymphocyte) resets the set point

Innate (Nonspecific) Defenses

• Interferons

• Polypeptides produced by viral infected cells that interferes with the ability of a second unrelated strain of virus to infect other cells

Inflammation

• Redness - vasodilation - histamine & Kinin (bradykinin)

• Pain - kinins (bradykinin) & histamine

• Swelling - edema

• Heat - vasodilation

Complement

• At least 20 proteins in the plasma

• Amplifies the inflammatory response

• Kills bacteria and foreign cells by lysis

• Acts with specific and non specific defenses

Complement Activation

Adaptive (Specific) Immunity

• Often non specific defenses are not enough to prevent microbes from taking hold.

• Specific defenses rely on antigens

Adaptive (Specific) Immunity

• Antigens

• Large protein molecules (or glycoproteins) found on the surface of an invader (cell surface label)

• Large complex molecules may have a number of different antigenic determinant sites

• We recognize our own antigens from foreign antigens

Adaptive (Specific) Immunity

• Haptens

• Small organic molecules which are not antigenic

• Can become antigenic by binding to proteins

• Creates antigenic determinant site

Lymphocytes

• Lymphocytes like RBCs are derived from stem cells of red bone marrow

• Precursors for lymphocytes spread via the circulatory system to thymus, spleen & lymph nodes

• Produce self-replacing lymphocyte colonies

Lymphocytes Precursors

• T lymphocytes or T cells

• Thymus can also seed other organs

• T cells - 65-85% of lymphocytes in the blood & most in lymph nodes

• Attack host cells which are infected

• Cell Mediated Immunity

• They physically attach to & destroy host cell

Lymphocytes - Bone Marrow

• Most lymphocytes which are not T lymphocytes are B lymphocytes

• B lymphocytes - B cells

• Antibody Mediated Immunity

• Antibodies

• Proteins which are capable of combining with and neutralizing antigens

Function of B Lymphocytes

• Exposure of B lymphocyte to antigen

• Initial encounter - Primary response

• Cell growth & many divisions (clonal selection)

• Memory cells & plasma cells

• Plasma cells - produce specific antibodies

• 2000/sec - 5 to 7 day life span

• Secondary Response

• Cell divisions - plasma cells and more memory B cells

Clonal Selection in B Cells

Antibodies

• Also called immunoglobins (Igs) - gamma globulin component of blood proteins

• Characteristic Y shape

• Antibodies bind with and neutralize antigens

• Form antigen-antibody (immune) complexes

• These are eventually engulfed by phagocytes

Basic Antibody Shape

Mechanisms of Antibody Action

Complement Fixation

• When antibody binds to antigen - antibody changes shape - exposes complement binding site

• Complement now is fixed to antigenic cells surface - eventually lysis occurs

• Also many molecules released - amplify inflammation, promote phagocytosis by opsonization (coats foreign invader with complement/antibodies)

Functions of T Cells

• Cytotoxic T (Killer) Lymphocytes

• Destroys specific victim cells that are identified by specific antigens on their surface

• Cell-mediated destruction

• T cells must physically attach to kill their victims

Functions of T Cells

• Cytotoxic T (Killer) Lymphocytes

• Destruction involves perforins - polymerize into channels

• Osmotic destruction

• Fight against viral & fungal infections, transplant rejection reaction & cancer cells

• Also some bacterial cells

Other T Lymphocytes

• Helper T lymphocytes (cells)
Suppressor T cells
Both regulate immune response to regulating B cells & Killer T cells

• Natural Killer cells (NK) - type of lymphocyte - destroy tumors in nonspecific fashion also some viral infected cells

Clonal Selection of Cytotoxic T Cell

Central Role of T Cells

Cytotoxic T Cell Attack

Cytokines

• Chemical mediators of cellular immunity

• Interferons - a, b, g - antiviral effects & enhance B & T cell function

• Interleukins

• Interleukin 1 - by macrophages & other cells - activates the T cell system

• Interleukin 4 - (B cell stimulating factor) - secreted by T cells & is required for proliferation & clone development of B cells

Cytokines

• Interleukins

• Interleukin 2 - released by Helper T cells - activation of Killer T cells & more

• Granulocyte colony-stimulating factor (G-CSF) & Granulocyte-monocyte colony-stimulating factor (GM-CSF) - promote leukocyte development & are used in medical treatments