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Defense against infectious disease. 6.3. WHAT’S THIS….?!. E. coli!!. ANYBODY KNOW….??. E. Coli is a bacteria. Bacteria (like E. coli), viruses, protozoa, fungi and even WORMS are various types of pathogens. . But wait…what the heck is a pathogen?!. But wait…what the heck is a pathogen?!.

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what s this


E. coli!!


e coli is a bacteria

E. Coli is a bacteria

Bacteria (like E. coli), viruses, protozoa, fungi and even WORMS are various types of pathogens.

But wait…what the heck is a pathogen?!

but wait what the heck is a pathogen

But wait…what the heck is a pathogen?!

Any living organism or virus that is capable of causing a disease is called a pathogen.

so what happens when the pathogen enters our body

So what happens when the pathogen enters our body?


If the pathogen is a bacteria, we can take antibiotics.

How are antibiotics effective against bacteria?

And why are antibiotics NOT effective against viruses?

bacteria are cells meaning they have different characteristics from our body cells which are cells

Bacteria are __________ cells, meaning they have different characteristics from our body cells which are __________ cells.





Antibiotics are designed to target the cell wall of bacteria pathogens so as not to harm our own body cells which do not have a cell wall.

These prokaryotic bacteria cells capable of causing a disease have a cell _____.

An antibiotic may have the purpose of blocking protein synthesis in bacteria, but not effect our own body’s cell’s ability to do the same task.

An antibiotic may inhibit the production of a new cell wall by bacteria, discontinuing the ability for the bacteria to grow and divide.



Viruses use our own body cells’ metabolism to create new viruses.

This means that any chemical with the goal of inhibiting the virus would, at the same time, damage our own body cells.

Viruses are a different story….

Thus…antibiotics are chemicals with the ability to damage/kill prokaryotic cells, but not eukaryotic cells or their metabolism.

Moving on 6.3.3

We can’t always avoid pathogens, but the human body fends off pathogens in some pretty sweet ways. Let’s take a look!


The top layer, the ____________ is constantly being replaced as dermal cells die and move upward. As this layer is not truly alive, it is the perfect barrier for pathogens.


The underneath layer is the dermis and is alive. This layer contains sweat glands, capillaries, sensory receptors and dermal cells that give structure and strength to the skin.


Stomach acid

Pathogens entering the body in food and water are usually killed by the acidic environment of the stomach.



Routes of aerial pathogen entry are lined with mucus

This can trap incoming pathogens and prevent them from reaching cells they could infect.

Mucus membranes are found in the trachea, nasal passages, urethra and vagina.

The cells that secrete the mucus also secrete an enzyme called lysozyme.

Some mucus membranes are lined with cilia.

Cilia are hair-like extensions capable of wave-like movement, pushing pathogens up and out.

Lysozyme can chemically damage many pathogens.

Cells of mucus membranes produce and secrete a lining of sticky mucus.


Our bodies house many types of leucocytes, white blood cells, which help us fight off pathogens in many different ways.

Macrophages are one of these types of leucocytes. Let’s take a closer look…


Macrophages are large white blood cells that are able to change their cellular shape to surround an invader and take it in through the process of ___________.


Macrophages are able to recognize if a cell is a natural part of the body or is ‘____’, or not part of the body, ‘___-____’ by examining the protein molecules that make up part of the surface of the cell/virus.





If the cell in question is determined as ‘self’, then it is left alone.

This type of response by the body is called ___-________ because the identity of the pathogen has not been determined at this point.

If a macrophage encounters a ‘not-self’ element, the macrophage will engulf the pathogen via phagocytosis.





Protein molecules that we produce in response to a specific type of pathogen.



Each type of antibody is different because each type has been produced in response to a different ________.


The cellular invaders, like bacteria, have proteins that are embedded into their outer surface.

These foreign proteins are called ________.



The similar Y shape of all antibodies lend themselves as binding sites where the antibody attaches itself to the antigen.

Each antibody is different and is specific for one type of antigen.

Because the antigen is a protein on the surface of a pathogen the antibody becomes ________ to the pathogen.


But how are these antibodies produced…? 


B Lymphocytes

The leucocytes, white blood cells, that produce antibodies are called B lymphocytes. There are many types of B lymphs.

Each type of B lymph can produce one type of antibody.

Only a small number of the needed antibodies for a specific infection can be produced because of this.

WAIT! Then how do the antibodies fend off the infection?!

Continue: THE STEPS


1. The specific antigen is identified.

2. A specific B lymph is identified that can produce the needed antibodies that will bind to the ________.


3. The chosen B lymph and several identical B lymphs clone themselves (through ______) to increase the number of _________ produced.




4. The newly formed B lymphs begin producing antibodies.

5. The new antibodies circle the bloodstream until the _______ match is found.



6. Using various mechanisms, the antibodies help eliminate the pathogen.

7. Some cloned antibody-producing lymphocytes remain in the bloodstream and give immunity from a second infection. They are called ________ cells.


And…THAT’S IT! Now you know how antibodies are produced!



HIV eventually leads to symptoms called

________ _______ ________ _________ (AIDS)

Human immunodeficiency virus






Helper-T cells communicate which cells need to undergo the cloning process and begin



Viruses, like HIV, must find a type of cell in the body that matches their own proteins in a complementary


One cell that has the needed proteins that HIV recognizes is the

helper-T cell.

Upon infection,

the helper-T cells

can no longer

communicate and antibodies are not produced.



The individual can no longer fight off pathogens and the symptoms of AIDS start to appear.

HIV has a latency period, it is many years after the infection that the symptoms develop.





It is difficult to find a vaccine or cure for the infection caused by HIV.

The virus mutates quickly, increasing the difficulty of HIV being stopped by the body’s immune responses or vaccines.

Associating HIV with drug use and sex only increased the obstacles preventing researchers from finding a cure. Today, however, large sums of money are donated to HIV/AIDS research.


HIV is transmitted from person to person by body fluids.

Sharing/reusing unsterile syringe needles, the exchange of body fluids during sex, and unchecked blood used in transfusions all lend themselves to the spread of HIV.

Today countries that are able to maintain reasonable medical care test blood frequently for blood-born diseases.

In the past HIV was associated with homosexuality. Today it is known that everyone is at risk of this disease.


Individuals who are HIV positive may

be discriminated against when it

comes to employment opportunities,

educational access, social acceptance

and many other forms of discrimination.

REMEMBER! Not all countries have access

to education and medical facilities

to deal with this disease.

Countries that are so

unfortunate as to

not have these amenities often group the infected patients together which leads to an exchange of diseases between them.


How can we delay the spread of this disease until a cure is found?




    • risk
  • exposure

The process of blood clotting

Blood escapes when capillaries, arterioles and venules are broken. Blood clots to “seal” the damaged blood vessels. This prevents excessive blood loss as well as pathogen entry.

Circulating in the blood plasma are plasma proteins. Two clotting proteins are:

(let’s see who remembers)




These factors are always present in the blood plasma.





Platelets are also always circulating the bloodstream. Platelets are cell fragments that form in the bone marrow. A large cell breaks into many pieces, creating the platelets.

Platelets do not have a ________ and have _____ cellular life spans of about 8-10 days.




The Process of Blood Clotting

Damaged cells of the broken blood vessel release chemicals that stimulate platelets to adhere to the area.

Platelets gather.

A plug begins to form. The damaged tissue and platelets release chemicals called clotting factors who convert prothrombin to _________.

Thrombin is an active enzyme and catalyzes the conversion of fibrinogen to ______.



Fibrin is relatively insoluble and forms a “meshy” network, stabilizing the clot.


Circling back to the immune responses from 6.3

Early in life the immune system only knows “self” and “not-self”.

Macrophages encounter a pathogen, engulfing the invader through phagocytosis if it is “not-self”.

After digestion, molecular pieces of the pathogen are displayed on the cell membrane of the macrophage. This is called ______ ___________.




Now, as the antigen had been identified, the helper-t cells turn the immune response from non-specific to _______-specific.

Leucocytes known as _____-__ cells recognize the antigen and are activated.




Helper-T cells chemically communicate with the specific B cell type to enable the production of the needed antibody.


Clone Selection

Mitotic divisions of the selected B cells create _________ cells in a process known as cell cloning.


There are two types of B cell:

Antibody-secreting plasma cells

--These cells immediately secrete antibodies to help fight off the first infection.

Memory cells

--These cells do not secrete antibodies during the first infection. Long-lived cells that wait for a second infection.



The immune system must be challenged by an antigen during the first infection in order to develop an immunity. All the cellular events are part of the response which leads to ________ to this pathogen.



This term best describes the identification of the leucocytes that can help with a specific pathogen and the multiple cell divisions which occur to build up the numbers of that same cell type.



These are the cells that provide long-term immunity. You must experience a pathogen once in order to produce these cells and have true immunity to that specific pathogen.


Active & Passive Immunity



Active immunity always leads to the production of memory cells and thus provides for a long-term immunity to a pathogen.

Passive immunity is when one organism acquires antibodies which were produced in another organism.

Only the organism that produced the antibodies has long-term immunity.


Examples of Passive Immunity

Transfer of antibodies from mother to fetus through the placenta. Memory cells are not transferred and thus only short-term protection is gained.

Acquisition of antibodies from the mother’s colostrum. Colostrum is the breast milk produced in late pregnancy and the first few days after birth.

Injection of antibodies in antisera. Examples of antisera include, most commonly, the antivenoms produced for treatment of poisonous snake/spider bites. Primary immunity would take too long.


Polyclonal & monoclonal antibodies

A primary immune response by an organism is called a polyclonal response.

The pathogen is typically being recognized as many antigens and not just one.

Each of the protein types can cause an immune response, so several kinds of B cells undergo clonal selection  several different kinds of antibody are produced.

Once a polyclonal immune response has occurred, it is difficult to separate the different kinds of antibody.

Scientists can form ‘pure’ antibodies all of the same type – monoclonal antibodies.


Production of monoclonal antibodies

1. Injection of an antigen into a lab animal (mouse).

2. The animal is given time for a primary response.

3. The spleen of the lab animal is ‘harvested’ to access enough blood cells.

4. Identifying the B cells that produce the targeted antibody are difficult to find.

5. Fusing the B cells with cancerous cells keeps them alive longer. The fused hybrid cells are called ____________.


6. The entire mix of cells is transferred to an environment where only the hybridoma cells can survive.


7.Individual hybridoma cells are separated and tested for the desired antibody. This test is called _______ (enzyme-linked immunosorbent assay).


8. When kept in an ideal environment, the hybridoma cells are virtually immortal.

Phew, goodness gracious. Why in the world would you even need monoclonal antibodies….??

Let’s see…



A common use of monoclonal antibodies is pregnancy testing. Only pregnant women have the human chorionic gonadotrophin (HCG) hormone because it is a hormone produced by the embryo. Hybridomas produced thanks to a lab animal that was injected with HCG will have B cells that secrete antibodies who recognize HCG as an antigen.

The anti-HCG antibodies are chemically bonded to an enzyme which catalyses a color change when the antibody encounters HCG molecules.



When body cells become cancerous they produce cancer cell-specific antigens on their cell membranes. Monoclonal cells that target the cancer-cell antigens is a possible treatment. This would target cancer cells specifically and would require less toxins and radioisotopic elements.


How does a vaccine result in immunity

You cannot be immune to a pathogen before being exposed to it at least once.

For some diseases, vaccines have been developed.

A vaccine is developed by weakening a pathogen and then injecting the pathogen into the body.


Producing a vaccine

-Selecting a particular ‘weak’ strain of a


-heating the pathogen

-chemical treatment of a pathogen

A vaccination

does not prevent

an infection, but on

subsequent exposure to

the real pathogen, the

secondary immune response is

quicker and more intense than the

primary immune response.




Possible total elimination of the disease. (smallpox)

Prior to 1999, many vaccines contained thimerosal, a mercury-based preservative.

Decrease in spread of epidemics and pandemics.

Multiple vaccines given to children in a relatively short period of time may ‘overload’ their immune system.

Preventative medicine is typically the most cost-effective approach to healthcare.

Anecdotal evidence suggested that MMR (measles, mumps, ruella) vaccine may link to onset of autism.

Each vaccinated individual benefits because the full symptoms of the disease do not have to be experienced to gain immunity.

Allergic reactions & autoimmune responses.