What is Immunity?

Resistance to a disease causing organism or harmful substance
• Two types
• Active Immunity
• Passive Immunity

Plants and animals have what is called innate immunity. Innate immunity is the first line of defense against pathogens. It involves several cell types, proteins, and even an organ. The organ involved is your skin. Yes, skin is part of the first line of defense. It protects you and prevents pathogens from getting inside your body.

So, what are some ways a pathogen gets inside? Air, food, or a break in the skin are some ways a pathogen enters. A pathogen entering through food or air has mucus to go through. The mucosal surfaces prevent pathogens from attaching to cells and causing disease. A set of proteins called the complement system is also involved. The complement system attacks the pathogen and marks it for destruction.

A pathogen getting through skin and mucus will have to deal with several types of cells including phagocytes, eating cells, and natural killer (NK) cells before it can cause disease. Pathogens have warning flags on their surface that say: 'I don't belong here'.

Neutrophils, macrophages, and dendritic cells are all phagocytes. They recognize the warning flag, attack the pathogen, and eat it - a process known as phagocytosis. If a pathogen is too big for one cell alone, several cells attack at once.

NK cells on the other hand, identify infected cells (host cells) and activate the host cell's death receptor pathway or give the cell a lethal injection (injecting enzymes that degrade proteins). Host cells even try to fight back by turning off machinery that would help the pathogen and sending out distress signals.

If pathogens make it through all this, it's time for adaptive immunity to step in, and they do this with the help of dendritic cells.
Immunity means being protected from something and being unaffected or not bothered by it. Let's say you have immunity to heat - this means heat can't bother you whatsoever - walking up to hot molten lava (about 2,000 degrees F!) would be no different than walking up to a river.

Active Immunity: (You) The body produces the antibodies
• Your body has been exposed to the antigen in the past either through:
• (Natural)-Exposure to the actual disease causing antigen
• (Induced)-Vaccines: are antigens are deliberately introduced into the immune system to produce immunity
• Because the bacteria has been killed or weakened, minimal symptoms occur
• Have eradicated or severely limited several diseases from the face of the Earth, such as polio and smallpox