Lymphatic System and Immunity

Nestor T. Hilvano, M.D., M.P.H.

Learning Objectives1. Describe the components and functions of the lymphatic

system. 2. Discuss the cells involved in the lymphatic system. 3. Describe the lymphatic tissues and organs as to structure

and functions. 4. Differentiate the body’s nonspecific and specific defenses.

5. Identify the forms and properties of immunity. 6. Distinguish between cellular immunity and humoral

immunity.7. Describe the structure of an antibody and discuss the

types of antibodies.8. Explain the primary and secondary responses to antigen

exposure.9. Discuss briefly autoimmune disorders, immunodeficiency

diseases, and allergies and give examples of each type.

Lymphatic System • Components

____ - clear colorless fluid similar to plasma, no cells except lymphocytes

____ - carry lymph from peripheral tissues to veins

____- are distributed throughout the body • Functions: Immunity, Lipid absorption (lacteals in SI),

Fluid recoverya. Lymphatic tissues & organs

b. Lymph

c. Lymphatic vessels

Lymphatic Capillaries

• Closed at one end

• thinner wall, larger diameter, flat or irregular in section

• Endothelial cells loosely overlapped - allow fluid, bacteria, viruses and cells entrance

- creates valve-like flaps (prevent return to ICS)

Route of Lymph Flow• Collecting vessels: course through many lymph

nodes• Lymphatic trunks empty into 2 Collecting vessels:

a) Rt. Lymphatic duct - drain the right side of head, neck, UE, and thorax

b) Thoracic duct - drain the rest of the body * cisterna chyli – expanded, saclike chamber

• What condition results from blockage of lymphatic drainage from a limb?

a. lymphadenopathy b. lymphedema c. lymphoma d. sarcoma

Cells of Lymphatic System• Circulating Lymphocytes, 3 types

a) ____ - natural killer cells, 5% to 10% of circulating lymphocytes, responsible for immune surveillance; attack foreign cells, virus cells, and cancer cells.

b) ____ - Thymus- dependent, 80%, 3 main types: cytotoxic, suppressor, helper; CMI

c) ____ - bone marrow- derived, 10% to 15%, differentiate into plasma cell, HI • Antigen Presenting Cells (APC) – macrophages in

epidermis, mucous membrane, and lymphatic organs

a. B cell b. T cell c. NK cell d. APC cell

Structures of Body Defenses• Lymphatic tissues – unencapsulated

a) MALT (GALT) – diffuse LT

b) Lymphatic nodules– has central, pale zone called germinal center- clusters found in ileum (called Peyer’s patches) and

appendix (aggregated lymphatic nodules) • Lymphatic organs - encapsulated

– Thymus– Red BM– Spleen– Lymph nodes– Tonsils

Thymus• Located in the mediastinum; primary lymphoid

organ • Atrophies after puberty • Functions: Cellular Immune Response• Septa divides Thymic lobes into lobules containing

an outer, thymic cortex and inner, thymic medulla• Reticular epithelial cells in cortex maintain blood –

thymus barrier. • Hassall's bodies (thymic corpuscles) – acidophilic

mass located in thymic medulla.

Lymph Node• Filters lymph (removes debris, pathogens,

antigens)

• Widely distributed lymphoid organs

• Subdivided into cortex and medulla

* germinal centers for B cell activation

• _______ - enlargement of lymph nodes

• Common site for metastatic cancer

Spleen• Located at left hypochondriac

• Structures made up of:

– Red pulp: sinuses filled with erythrocytes

– White pulp: resembles lymphoid nodules

• Functions – removal of RBC/blood components, storage of iron recycled from RBC, and immune response

Tonsils• Pathogens get into tonsillar crypts and

encounter lymphocytes

• ______ tonsils = posterior inferior margin of oral cavity

• ______ tonsils = base of tongue

• ______ tonsil = lie in the nasopharynx; also called the adenoid

a. lingual b. pharyngeal (nasopharyngeal) c. palatine

Defenses Against Pathogens• Nonspecific defenses - no prior exposure,

against any type of invading agent– physical barriers – phagocytic cells – immunological surveillance– fever– Interferon (produce antiviral proteins and

destruction of cancer cells)– complement– inflammation

Complement System• Proteins that complement antibody action• Classical pathway – fast method, C1 binds to

antibody molecule attached to antigen• Alternate pathway – slow method, exposed to

antigen, with factor P, B, and D• Both split C3 into C3a and C3b

- stimulation of inflammation, attraction and enhancement of phagocytes, and cytolysis.

Inflammation• Defensive response to tissue injury

1.limits spread and destroy pathogens

2.removes debris

3.initiates tissue repair

• Cardinal signs- rubor: _________ - tumor: ________

- calor: _________ - dolor: _________

a. pain b. redness c. swelling d. warm (hot)

Specific Immunity• Properties of immunity: specificity,

versatility, tolerance and memory• 2 types of specific immunity:

cellular and humoral• ___ – complex molecules that trigger

an immune response• ___ – protein molecules that fight

against an invaders a. Antibody (immunoglobulins) b. antigen

Active and Passive Immunity• ____- Natural active immunity

– develops as a result of natural exposure to antigen

• ____- Artificial active immunity – develops after administration of antigen to prevent

disease

• ____- Natural passive immunity – acquires antibodies from mother

• ____- Artificial passive immunity – conferred by administration of antibodies

a. DPT vaccination of children b. Injection of antirabies immunoglobulins c. Immunity conferred after recovery from pulmonary tuberculosisd. Maternal antibodies transferred to infants at birth

Comparison of B and T Cells

Antigen-Presenting Cells• Function depends on MHC proteins (membrane

glycoprotein)

– act as cell ID tag• Specialized cells responsible for activating

T cell defenses• Include all the phagocytic cells. • Antigen bound to MHC proteins – activates

immune system to destroy abnormal cell or dangerous antigen

Cellular Immunity

• T cells• 3 stages – antigen recognition, attack, and

memory• CD8 = cytotoxic T and suppressor T cells• CD4 = helper T cells• Memory T cells • Organ transplant problem = ___________

Humoral Immunity• Recognition

– B cell receptors bind antigen, take in and digest antigen then display epitopes on its MHC-II protein

– After co-stimulation by TH cell, divide repeatedly, differentiate into plasma cell, produce ____________ specific to that antigen

• Attack– antibody bind to antigen, render it harmless,

‘tag it’ for destruction• Memory

– some B cells differentiate into memory cells

Antibody Structure

• Ag binding site = free tips of variable segments

• variables = confer specificity of an antibody

• constant = form the base of the antibody; basis of classification of antibodies

Antibody Classes• IgA: monomer in plasma; dimer in secretions

• IgD: monomer; B cell membrane Ag receptor

• IgE: monomer; on mast cells and basophils;

stimulates release of ________________;

important in immediate hypersensitivity.

• IgG: monomer; 80% circulating, crosses placenta, 2 immune response

• IgM: pentamer, 10% in plasma, 1 immune

response, agglutination of ABO blood group,

complement fixation

Humoral Immunity - Attack• Neutralization

– antibodies mask pathogenic region of antigen

• Complement fixation– antigen binds to IgM or IgG, antibody changes shape,

initiates complement binding

• Agglutination– antibody binds to multiple enemy cells immobilizing

them forming large complexes.

• Precipitation– creates antigen-antibody complex that precipitates

Humoral Immunity Responses

• _______ response – peak response takes 2 weeks to develop, decline rapidly

• _______ response – activates memory B cells, IgG rises quickly

a. Primary responseb. Secondary response

Hypersensitivity (Allergy)• Type I – immediate hypersensitivity; Antibody mediated = IgE

* allergic rhinitis; asthma; anaphylaxis• Type II – cytotoxic reactions, Antibody mediated

(IgG, IgM) * binds to antigens on cells; complement

activation and lyses or opsonization • Type III – Immune complex, Antibody mediated

(IgG, IgM) * complexes precipitate and trigger inflammation

• Type IV – delayed hypersensitivity, Cell mediated* 12 to 72 hour delay

Immune Disorders

• Autoimmune diseases = production of autoantibodies; RA, IDDM, thyroiditis

• Immunodeficiency diseases = SCID, HIV, or exposure to immunosuppressive agents

- HIV transmission: ________________

- Undamaged latex condom is an effective

barrier to HIV

Homework (Self-Review) 1. Define key terminologies: pathogen, lymphedema,

lymphadenopathy, antigen presenting cell, innate immunity, nonspecific immunity, antigen, antibody.

2. Differentiate humoral immunity and cellular immunity as to type of lymphocyte, antigen acted on, product of secretion, and mechanism of action.

3. Describe the forms of active and passive immunity by noting an example.

4. Give the function of the following: germinal center, NK cell, interferon, plasma cell, lymph node, spleen, thymus, and red bone marrow.

5. Describe the cardinal signs of inflammation and how it respond to tissue injury.