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�� Unit 1: Nature of the Immune System ��Part 1: Introduction and Historical Concepts�

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Introduction

Immunology is a relatively new field
Entire history recorded in the last 100 years
1960s cells of immune system identified and characterized
Tests developed to detect presence of immune substances in the blood

In the entire scheme of studying the human body, immunology is a relatively new field. To put this in perspective a little bit, even ancient Egyptians were analyzing urine characteristics. So for centuries and centuries scientists have been researching the greatest machine of all, which is the human body. But as far as our immune system goes – the entire history of this has only been recorded in the past 100 years or so. If you think about it, it wasn’t that long ago that masses of people died from things we take for granted as having controlled: smallpox, polio, rubella, blood transfusions, mom/baby incompatibilities, organ transplantation, treating cancer, treating HIV, treating autoimmune disease, etc.

All of these things have to do with studying the immune system. Once the cells of the immune system were identified and characterized in the 1960s, then came testing. Now that we know what causes most of these things, we can work toward testing to diagnose and ultimately prevent them. One of the main ways we diagnose diseases immunologically is by testing for either antigens or antibodies in a person. Antigens and antibodies will be explained in further detail throughout this unit. Other ways are to test for CD markers on the surface of cells, measure cytokine levels, or nowadays do molecular testing.

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What You Need To Know

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Immunity

Immunology defined as the study of the reaction of a host when foreign substances are introduced into the body
Antigen is the substance recognized as foreign to the body which causes an immune response
Immunity is the condition of being resistant to infection
Serology is the study of the non-cellular components (serum) in the blood

The immune system has two goals: 1) To be able to recognize self vs. nonself, and 2) defend against nonself. Your body needs to be able to distinguish between what belongs to you, and what is foreign. Another way of saying this is that the immune system should tolerate self, meaning it should not react against self. In an autoimmune disorder, the body fails at this first job – it lacks self-tolerance (sees itself as foreign) and starts attacking things that belong to self.

The word antigen literally means ANTIbody GENerating factor. An antigen is anything that stimulates your body to make an antibody. An antigen can be foreign, or it can belong to self. So the key word here is “recognized” as foreign. Antibodies made to a particular antigen should protect you the next time you get exposed to that same (or even similar) antigen.

You can possess immunity through a few different mechanisms:

You got exposed to an infection and actually made your own antibodies (termed active immunity)
You received a vaccine which tricked your body into thinking you got exposed to a virus/bacteria and you made your own antibodies (another form of active immunity)
Mom passes her antibodies to her baby either in utero or after birth via breastmilk (termed passive immunity)
You get injected with antibodies someone else made to a disease – like what you’ve seen lately with treating COVID-19 patients with convalescent serum (another form of passive immunity)

Active immunity is more-or-less lifelong immunity. Antibodies levels do drop off as we age, but for simplicity’s sake we’ll say lifelong immunity. Passive immunity is temporary. Maybe lasting 3-4 months at the most.

Serology is also the name of the lab department that diagnoses infectious diseases with tests based on antigen/antibody reactions.

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Immunization/Vaccination

Purposeful exposure of individual to infectious material to elicit immunity
Early forms of vaccination were developed in ancient China as early as 200 B.C.
People inhaled powdered scabs from people infected with smallpox to protect against the disease

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Vaccination – Edward Jenner

Smallpox affected all levels of society
Jenner noticed that milkmaids did not generally get smallpox
Jenner theorized that the pus in the blisters which milkmaids received from cowpox (a disease similar to smallpox, but much less virulent) protected the milkmaids from smallpox

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Vaccination – Edward Jenner

Inoculated 8-year-old with material from pus in cowpox blisters
Exposed boy to infectious agents and no disease followed
Jenner's unique contribution was not that he inoculated a few persons with cowpox, but that he then proved they were immune to smallpox
Process called vaccination, from vacca, Latin for cow

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Ethical Smallpox Issue

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“Last Samples of Smallpox Pose a Quandary”�

This article was written before 9/11 but it is still a thought-provoking article. https://www.smithsonianmag.com/science-nature/should-we-destroy-our-last-living-samples-virus-causes-smallpox-180951321/
What are your thoughts? Post them to the Discussion Board in Blackboard.

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Vaccination

A vaccine - biological preparation that elicits immunity to a particular disease
A vaccine may be:

Weakened forms of pathogens
Killed or inactivated forms of pathogens
Purified material such as proteins which are similar to pathogens

Stimulates the body's immune system to recognize the agent (antigen) as foreign, destroy it, and "remember" it, so that the immune system can more easily recognize and destroy any of these microorganisms that it later encounters

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Vaccination - Types

Killed microorganisms
Attenuated – live organisms cultivated to disable virulent properties (MMR, yellow fever vaccines)
Toxoid – inactivated toxic compounds in cases where these (rather than the micro-organism itself) cause illness (ex: tetanus/diptheria)
Subunit – fragments create an immune response
Conjugate – linking outer coats to proteins which can the lead immune system to recognize it-(Haemophilus influenzae type B)
mRNA - vaccine uses a copy of a messenger RNA to produce an immune response. (Covid vaccine)

In a killed microorganism preparation, all of the pathogen’s antigens are present.

Attenuated means changed. This can be achieved by heat, aging, or chemical means.

The tetanus and diphtheria vaccines are examples of toxoid preparations.

Regarding the conjugate mechanism: some things are too small for the immune system to recognize as foreign. These things are called haptens. If your body gets exposed to a hapten, it would not elicit an immune response (antibody production) because it would “fly under the radar” so to speak and go undetected. So haptens have to be coupled with something (usually a protein) to make themselves bigger, which would lead to immune system stimulation.

Subunit vaccines use only part of a target pathogen to provoke a response from the immune system. This can be done by isolating a specific protein from a pathogen and presenting it as an antigen on its own. The acellular pertussis vaccine and influenza vaccine (in shot form) are examples of subunit vaccines. Another type of subunit vaccine can be created via genetic engineering. ie. HPV

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Rabies

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Rabies

A viral disease that causes acute encephalitis (inflammation of the brain).
It is zoometric (i.e., transmitted by animals), most commonly by a bite from an infected animal but occasionally by other forms of contact
The period between infection and the first flu-like symptoms is normally two to twelve weeks, but can be as long as two years
Rabies is almost invariably fatal if post-exposure prophylaxis is not administered prior to the onset of severe symptoms

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Rabies

Louis Pasteur applied the principle of attenuation to a rabies vaccine
Developed a rabies virus that was milder and had a shorter incubation period than the wild virus
A person bitten by a rabid animal would be inoculated with the Pasteur virus and rapidly develop immunity to the wild strain�

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Rabies

He developed his rabies vaccine by growing the virus in rabbits, then drying the affected nerve tissue (spinal cords) to weaken the virus
On July 6, 1885, the vaccine was administered to a 9-year-old boy who had been attacked by a rabid dog
The boy survived and avoided contracting rabies, which would have almost certainly proved fatal
http://www.historylearningsite.co.uk/louis_pasteur.htm