The immune system is a set of mechanisms that protect an organism from infection by identifying and killing pathogens. This task is extremely difficult, since pathogens range from viruses to parasitic worms and these diverse threats must be detected with absolute specificity amongst normal cells and tissues. Pathogens are also constantly evolving new ways to avoid detection by the immune system and successfully infect their hosts. To meet this challenge, multiple mechanisms have evolved to recognize and neutralize pathogens. The immune systems of vertebrates such as humans consist of many types of proteins, cells, organs, and tissues, which interact in an elaborate and dynamic network. As part of this more complex immune response, the vertebrate system adapts over time to recognize particular pathogens more efficiently. The adaptation process creates immunological memories and allows even more effective protection during future encounters with these pathogens. This process of acquired immunity is the basis of vaccination.

Read the rest of this article: http://en.wikipedia.org/wiki/Immune_system

_______________________________ Today's selected anniversaries:

1700: Sweden introduced its own Swedish calendar in an attempt to reform into the Gregorian calendar. (http://en.wikipedia.org/wiki/Swedish_calendar)

1872: Yellowstone National Park, the first national park in the world, was established. (http://en.wikipedia.org/wiki/Yellowstone_National_Park)

1896: Ethiopia won the decisive Battle of Adowa over Italy, ending the First Italo-Abyssinian War. (http://en.wikipedia.org/wiki/Battle_of_Adowa)

1919: Korea under Japanese rule: The Samil Movement began with numerous peaceful protests in Korea, but was brutally suppressed by the Japanese police and army. (http://en.wikipedia.org/wiki/March_1st_Movement)

1954: The 15-megaton hydrogen bomb Castle Bravo was detonated on Bikini Atoll in the Pacific Ocean, resulting in one of the worst cases of radioactive contamination ever caused by nuclear testing. (http://en.wikipedia.org/wiki/Castle_Bravo)

_____________________ Wikiquote of the day:

We should not be simply fighting evil in the name of good, but struggling against the certainties of people who claim always to know where good and evil are to be found. -- Tzvetan Todorov (http://en.wikiquote.org/wiki/Tzvetan_Todorov)