Autoimmune diseases attack the body's immune system instead of disease.
http://www.pspinformation.com/disease/immunesystem/immune.shtml
Through mutation, some bacteria 'adapt' their structure to create new generations of bacteria that are 'resistant,' meaning they cannot be killed by antibiotics. These resistant bacteria have been given the nickname 'superbugs.'
http://www.pspinformation.com/disease/immunesystem/superbugs.shtml
Antibiotics can impair the body's immune system. Some antibiotics reduce inflammation which then prevents white blood cells from attacking and killing harmful bacteria.
http://www.pspinformation.com/disease/immunesystem/supergerms.shtml
Study of tea use suggests chemical in beverage may boost immune systems.
http://www.pspinformation.com/disease/immunesystem/tea.shtml