Have you ever wondered how an organism can "fight off" an infection? Why are some infections worse than others? Why are so many scientific studies, including immunology studies, done on other organisms?

In this lesson you will look at the structures and functions of the immune system that react to fight these infectious diseases. 

Look at the photo below and answer the questions.

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On the prior page, you were looking at a photo of cells in a mouse. 

You may have guessed that those large green cells were part of the immune system, as you watched it engulf the smaller red circle. In fact most organisms have some types of cells that provide a defense against invaders. A general term for these cells is phagocytes, which comes from the Greek root phagein, "to eat" or "devour", and "-cyte", the suffix in biology denoting "cell."

Phagocytes were discovered by Elie Metchnikoff in the 1880s. Watch the video below to see his experiments that led to discovering them. 

sea star phagocytes original exp from Lauren Levites on Vimeo.

In the model below, discover what happens to the individuals in the sea star population when exposed to harmful bacteria. These phagocytes are part of the innate immune system. These cells provide non-specific responses, which means they respond to anything they view as foreign or an invader.

The Innate Immune System: 

The innate immune system is characterized by general, non-specific responses. The non-specific response is part of the innate immune system. Responses include sneezing, coughing and diarrhea. 
Physical barriers, such as the skin, also contribute to innate immune protection.
The innate immune system also protects us with chemicals such as acids in the stomach and enzymes in tears. 

We've been looking at a non-specific immune response, as phagocytes will move in to gobble up all types of invaders. But, how do some organisms become immune to specific diseases? That requires another level of immunity, called the adaptive immune system.

The adaptive immune system is mainly seen in vertebrate organisms. Although, there is some current research that points to some features possibly in invertebrates, like insects. 

Use the model below to discover one of the major features of the adaptive immune system: 

The Immune System:

These two parts of the immune system, innate and adaptive, do not work separately. They overlap and support one another through chemical signals sent via the bloodstream and lymph nodes. So, the next time you feel your heartbeat or you breathe, remember that your immune system is working just as hard, if a bit more slowly—it’s certainly helping to keep you healthy! 

The Adaptive Immune System:

Unlike the innate immune system, the adaptive immune system responds specifically to an invading virus or bacteria. The cells that contain the invading pathogen have an antigen, which the antibody responds to. Antibodies are the primary weapons of the immune system, since they are specifically designed to combat an invader. 
The adaptive immune response consists of B cells and T cells. 

• B cells make antibodies, while T cells show B cells what kinds of antibodies to make. 
• T cells also kill virus-infected cells, so that the virus can’t spread. 

B and T cells respond specifically to an invading organism, and remember when they have encountered a particular pathogen before. That way, when the pathogen invades the body again, the adaptive immune system can respond quickly and efficiently, preventing an infection. 

image source

Immune System Videos:

Ameoba Sisters Immune System

The Immune System: B Cell, T Cell, Soldier, Spy