1. Amazing videos to help with this if you want to cover this content in more detail:

2. Overview
One key component of maintaining homeostasis is protection against disease.
All organisms have disease-fighting mechanisms, but vertebrates specifically have immune systems
= network of organs that work together to recognize, fight, and defend against foreign substances at a cellular level
Important note: The immune system is one of the most AMAZING examples in our body of homeostatic regulation from a system level all the way to a cellular level.
Immune system is also unique compared to some of the other body systems because it utilizes organs and tissues that are in a variety of other systems – it is highly collaborative 

3. Overview Pathogens: organisms or viruses that can cause disease
Antigens: foreign substances that act as signaling molecules to induce an immune response in the body (such as the production of antibodies)
Antibodies: proteins used by the immune system to neutralize pathogens
Antigens are the part of the pathogen that your body learns to recognize.
Antigens aren’t ALWAYS toxins or related to pathogens. Ex. Blood Type! Your red blood cells have proteins on their plasma membranes that are antigens, and your body can only tolerate blood that has the same antigens as your blood cells. For example, Type A blood type means those people have A antigens on their red blood cells. This means if you take in Type A blood, your body recognizes it and receives it. If you were to take in Type B blood which has Type B antigens, your body would reject it because it has developed antibodies that are anti-B antigens, since those are considered foreign substances. People with Type AB blood have both A and B antigens present. Type O blood has no antigens which is why people of any blood type can accept it.

4. Overview
The goal of your immune system is to detect and deflect pathogens, but if that doesn’t work, it will then try to destroy them
White blood cells (lymphocytes) play a significant role in this. They produce antibodies, engulf invaders, tag pathogens for killing, and remember so that they can fight off future attacks.
Photo: The yellow is digitally colored to show Staphylococcus aureus bacteria and the blue are white blood cells that are about to destroy these bacteria.
Photo Credit: Frank DeLeo, National Institute of Allergy and Infectious Diseases (NIAID); obtained from the CDC:
Eventual hope is to reach immunity = when an organism
has developed enough defenses to successfully avoid an invasion from a pathogen

5. Innate Immunity 1st line of defense (external)
Skin = huge defense
Mucous membranes = line openings in the skin in order to protect respiratory, digestive, urinary and reproductive tracts
2nd line of defense (internal)
Fever
Increases metabolism of cells so they heal faster
Chemical signals
Inflammation
Acts like an internal fire alarm
Defensive cells (WBCs)
On the next two slides I am going to highlight two types of defensive cells – phagocytes and natural killer cells – but there are more!!

6. Phagocytes Defensive cells that eat pathogens to get rid of them
Ex. Neutrophils = the most abundant WBC  pus
Ex. Macrophages = use cytoplasmic extensions to reel in and “eat” bad stuff
Photo: Shows a mesothelial cell in a mouse ingesting a Orientia tsutsugamushi bacterium via phagocytosis
Photo Credit: CDC/ Dr. Edwin P. Ewing, Jr.,
Phagocytosis = the ingestion of pathogens

7. Natural Killer Cells
Defensive cells that can kill your own cells by triggering apoptosis if they see they are infected
Help with killing both tumors and virus-infected cells
Uses perforin (a protein) to create pores in the cell membrane of an infected cell through which they can inject enzymes that will stimulate the cell to do apoptosis
3D illustration shows lymphocytes (WBCs) like NK cells attacking cancerous cells.