Molecular mechanisms underlying CD27-CD70 costimulation

We are in a constant state of war, threatened by
both exogenous enemies in the form of killing
pathogens, or enemies from within in the form of
tumor cells. The key for survival of our species
amongst an overwhelming amount and diversity
of microorganisms, such as viruses, bacteria
and parasites is a well functioning immune
system. Essential for the immune system to
function properly is the ability to distinguish
between foreign agents, malignant cells and the
organism’s own healthy cells. The earliest written
mention of immunity goes back to 430 BC during
the plague of Athens when it was discovered
that people who had recovered from the disease
could nurse the sick without contracting the
illness a second time (1). However, it was not
until the 19th and 20th centuries before the
concept developed into scientifi c theory.
Two different types of immune responses can be
distinguished that are referred to as the innate
and the adaptive immune system. Usually,
physical barriers prevent pathogens like bacteria
and viruses from entering an organism, but if a
pathogen breaches these barriers, the innate
immune system provides an immediate albeit
non-specifi c response. The innate immune
system is thought to constitute an evolutionarily
old defense strategy and is found in all plants
and animals. Major functions of the vertebrate
innate immune system include the identifi cation
and removal of foreign substances, the activation
of the complement cascade, recruitment of
immune cells to sites of infection and activation
of the adaptive immune system through antigen
presentation (2,3).