Working togetherTHE LYMPHATIC AND IMMUNE SYSTEMS

Why do we need an immune system?

Yes, we do.

But: they are non-specific defenses.

Innate and acquired immunity

Review of Key Terms

Antigen

Antibody

Primary Reaction

Secondary Reaction

Macrophage

We need Specific Defenses too.

B cells and T cells accomplish this.

B cells are important for antibody induced immunity in body fluids

T cells are important for cell based immunity.

(Think abnormal cells and pathogens in cells)

First let’s Review Non-Specific Defenses: Integumentary system

Phagocytes in blood and tissues

Complement

Fever and Inflammation

But it is not enough!

3 Cell Types of the Immune SystemLymphocytes

“The militia”

Phagocytes

“The janitors”

NK cells

“The ninjas”

Phagocytes

First line of defense, often attack and remove microorganisms before lymphocytes (T cells and

B cells) detect them.

2 Types

Microphages – patrol blood

Macrophages – patrol peripheral tissue

Specific Defense Cell 1: T cells

4 Types of T cells

Cytotoxic- highly mobile, seek out and destroy abnormal or infected cells

“think detective”

Helper- activate B cells so they are able to produce antibodies

“think keys”

Suppressor- Keep the immune system from overreacting

“think bouncer”

Memory- on 2nd exposure automatically transform to cytotoxic T cells.

Thymus dependent cells, recognize antigens when bound to special proteins in a cell membrane, called MHC proteins.

Specific Defense Cell 2: B cells

B memory cells – on second exposure they divide into plasma cells that secrete antibodies in massive quantities*.

*How massive?

-When stimulated by cytokines from a T cell, plasma cells can secrete up to 100 million antibody molecules an HOUR

B cells - Bone marrow derived cells, each carries its own specific antibody molecule that fits a corresponding antigen. Needs the Helper T cells to activate and stimulate their division. They will eventually divide into plasma cells and Memory B cells.

2 types of B cells

T cell activation

When a macrophage (“think pac-man”)

engulfs a pathogen with an antigen on it, the antigens are presented to the T-cell by

placing them on its cell membrane at the MHC.

The T-cell then is able to recognize and bind to the antigen there and begin dividing.

B cell activation On their surface B cells have specific antibodies

that bind with specific antigens.

B cells engulf the antigen and present it on their cell membrane to be recognized by an activated

Helper T cell, which gives the B cell the “go ahead”.

The T-cell attaches to the part of the B cell membrane where the antigen is and begins to secrete

cytokines to activate the B cell.

The B cell can now divide, accelerate plasma cell formation, and enhance antibody production.

Remember the difference!

Primary Response

- Antibodies do not peak until 1-2 weeks after exposure

- IgM are first to appear, but do not create memory cells. Immediate, but limited defense

- IgG rises more slowly and creates memory cells. Takes over response.

Secondary Response

- Even low antigen concentrations will immediately trigger memory B cell response.

- Antibodies increase rapidly and reach much higher concentrations than with the primary response

- Invading organism is often destroyed before symptoms appear.

Types of Antibodies

IgA – Found in secretions of the body.

IgD – Found on the cell membrane of B cells.

IgE – Found wherever IgA is. Thought to be involved in triggering allergic reactions.

IgG – Primarily recognizes bacteria, viruses, and toxins.

IgM – a very large antibody that binds to food and incompatible blood cells.

How Antibodies Attack Antigens

Phagocyte recognition and destruction

Antigens clump together and are targeted by macrophages

The toxic portion of the antigen is covered

Activate complement proteins that form holes in antigen

So, how does the lymphatic system fit into all of this?

It’s primary function is the production, maintenance, and distribution of lymphocytes!

Remember, those are the T cells and B cells essential for specific immunity.

Organs of the Lymphatic System

The organs of the Lymphatic System include:

Lymph

Lymphatic Vessels

Lymphoid Tissues

Lymphoid Organs

Lymphocytes

How does the Lymphatic system work?

More fluid is delivered to tissues than can be carried away.

The Lymphatic System’s circulatory network returns this fluid to the blood stream.

On the way to the major collecting ducts, pathogens are filtered at stops such as the spleen and lymph nodes

Lymphocytes, produced in the organs of the lymphatic system, freely flow through this circuit and patrol.

Formation of Lymphocytes

Two different types are produced in the bone marrow

One type stays there, the other migrates to the thymus to mature, separated from the blood.

When they have completed maturing they return to the bone marrow and lymphoid tissues and organs, such as the spleen.

Lymphoid Organs

All lymphoid organs are separated from the surrounding tissues by a fibrous connective tissue

capsule.

Lymph Nodes

Thymus

Spleen

What is lymph?

A thin, watery fluid originating in organs and tissues of the body.

It circulates through the lymphatic vessels and is filtered by the lymph nodes.

It enters the blood stream at the junction of the internal jugular and subclavian veins.

Flow of LymphLymphatic capillaries

Small Lymphatic Vessels

Superficial and Deep Lymphatics

Lymph Nodes

Major Lymph Collecting Ducts

The Filtering Process

Lymph nodes – Purify lymph before it returns to the venous circulation. 99% of the antigens are removed.

A T cell may spend 20 hours in a lymph node.

A B cell may spend 30 hours in a lymph node.

Other organs of the Lymphatic System

Thymus – the thymus provides a place for lymphocytes to mature, separated from the systemic circulation.

The thymus also produces several hormones that are important to the development and maintenance of a normal immune system.

Other Organs of the Lymphatic System

Spleen – Has the largest collection of lymphoid tissue in the body and does for blood what lymph nodes do for lymph.

-removal of abnormal blood cells and components

-storage of iron from recycled red blood cells

-initiation of immune response by B and T cells in response to circulating antigens.

Diseases of Immunity

HIVHuman Immunodeficiency Virus

Pathology of HIV

Depletes Helper T cells

Circulating antibodies also decrease, and cell mediated immunity is reduced. (As a result pathogens that are usually harmless create

opportunistic infections.)

The surplus in suppressor T cells as Helper T cells die turns off the normal immune response.

Immune surveillance is also decreased, increasing cancer risk.

Stages of HIVAcute Infection

Large amounts of the virus are being reproduced in the body.

Usually occurs within 2-4 weeks of infection

After rapid Helper T cell destruction, immune system kicks in and body returns to a viral set point.

Clinical Latency

HIV reproduces at low levels, but is still active

It is still possible to transmit the virus

This period may last 8 years or longer.

AIDS

Helper T cell count falls to dangerously low levels

At this stage the immune system is badly damaged and opportunistic infections are likely.

Survival is typically 3 years with AIDS. It is only 1 year with an opportunistic infection.

Surprising HIV Facts

Virus enters the body under clever camouflage, cloaked in sugar molecules.

There are different strains of the virus, some more deadly than others.

34 million people are living with HIV today.

Transmission to a fetus from the mother is now considered entirely avoidable with medication.

A quarter of AIDS deaths are from TB

Credits to:

Innocent Kingsely Asogwa

Bruno Thadeus

Analin Empaynado

Jefferey C. Pommerville