Introduction to Immunology: A Comprehensive Guide to the Immune System's Defenses, Exams of Immunology

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Introduction to Immunology

Passive Immunity- Immunity that is obtained from a

outside source. Example: Antibiotic, Clostrum

Active Immunity- Immunity that is obtained from the

immune system actively defending the body.

Example: Vaccines, Immunity after having a disease

Immunity

Pathogen- is any agent (bacterium, virus, etc)

that can cause us trouble

Nonspecific Defenses are the body's first line

against disease. They are not directed against a

particular pathogen. They guard against al

infections, regardless of their cause.

Specific defenses are attempts by the body to

defend itself against particular pathogens.

Since Pathogens must enter the body in order to

cause disease, the body's first line of defense is

to keep pathogens out. So, what organ is used

for this?

Basics and Terms

The Body's MOST IMPORTANT Nonspecific Defense is the SKIN. UNBROKEN Skin provides a continuous layer that protects almost the whole body. Very Few Pathogens can penetrate the layers of dead cells at the skin's surface. Oil and sweat glands at the surface of the skin produce a salty an acidic environment that kills many bacteria and other microorganisms. The importance of the Skin as a Barrier against Infections becomes obvious when a small portion of skin is broken or scraped off: Infection almost always follows. Infections are a result of the penetration of the broken skin by microorganisms normally present on the unbroken skin. Pathogens also enter the body through the Mouth and Nose, but the body has Nonspecific Defenses that protect those openings.

Basics continued

This is the SECOND LINE OF DEFENCE

When Pathogens get past skin and mucous

membranes, and enter the Body, this Second

Line of Defence comes into play, triggered by

injury to tissues in the body.

The injured cells release a protein called

HISTAMINE , which starts the a series of

changes called the Inflammatory Response.

The Inflammatory Response

The most common Phagocyte, 50 to 70 percent of the White Blood Cells in the body, is the NEUTROPHIL. Neutrophils circulate freely through blood vessels, and they can squeeze between cells in the walls of a capillary to reach the site of infection. They then engulf and destroy any pathogens they encounter

Inflammatory Response Continued

Another type of Phagocyte (also a White Blood Cell) is the MACROPHAGE ; they consume and destroy any pathogens they encounter, they also rid the body of worn out cells and cellular debris. Some Macrophages are stationed in the tissues of the body, awaiting pathogens, while others move through the tissues and seek out pathogens.

Inflammatory Response Continued

If a pathogen is able to get past the body's nonspecific defenses, the immune system reacts with a series of specific defenses that attack the disease causing agent.

This is called the IMMUNE RESPONSE

A substance that triggers the specific defenses of the immune system is known as an antigen.

An antigen is a substance that a macrophage (wbc) identifies as not belonging to the body.

But if all that is not enough …

The Immune Response involves several organs, as well as White Blood Cells in the Blood and Lymph. These include the BONE MARROW, THYMUS, LYMPH NODES, TONSILS, ADENOIDS, AND SPLEEN.

Each organ of the immune system plays a different role in defending the body against pathogens.

Bone Marrow manufactures the billions of WBC needed by the body every day. Some newly produced WBC remain in the bone marrow to Mature and Specialize , while others travel to the Thymus to Mature.

Lymph Nodes Filter Pathogens from the Lymph and expose them to White Blood Cells

The Spleen , a fist-sized organ located behind the stomach, Filters Pathogens from the Blood. It is stocked with WBC that respond to the trapped pathogens.

The Immune Response

The general idea is this:

Something has got through the first lines of defence, and entered the body in force.

If the body has been invaded by this particular

nasty thing before, then special Lymphocytes

called B-Cells and T-Cells are able to recognise

these specific pathogens, and overwhelm

them (thanks to the `immune system

memory’)

If this is a new invasion, then the B-Cells will

learn how to fight this invader. (and then

The Immune Response:

The last line of defence

Specific Antigen Recognition

B-cell or T-cell

Surface receptor molecule

Nasty thing This lymphocyte recognises the red pathogen

B-cell or T-cell

This one doesn’t

Generating variety II

In addition, B-Cells (but not so much T cells) also undergo somatic

hypermutation. Somatic just means in the body, during one’s lifetime.

Hyper just means `a lot’. In a nutshell:

1. A B-cell recognises an antigen
2. A complex chain of events then leads to this B-cell dividing, creating daughters who produce the same receptor.
3. But these daughter cells may have mutations in their library.
4. Some of the daughters may recognise the antigen even better.
5. Back to 1.

A pathogen comes along: If it gets through the barriers (skin, etc), nonspecific lymphocytes kill it, as part of the `inflammation’ response in reaction to injury. If it gets past that (I.e. there’s so much of it, it gets into the bloodstream anyway), then the Immune Response comes into play, as follows: If we’ve seen this one before , there are antibodies in the blood (secreted by memory cells); these antibodies disable and/or tag the invader. The tagging attracts killer cells to make sure it is destroyed. If we haven’t seen this before , B-cells and T-cells are floating around with a great variety of surface receptors. One of these will at least recognise it a bit. Clonal expansion then happens, and with gene variability and somatic hypermutation we eventually get some B or T cells which are capable of recognising it. The associated antobodies then disable and tag the invaders.

Summary