Page 200 - The Miracle in the Cell Membrane

icroscopic liv ing things that do not
belong to the body itself can enter it by
one means or anoth er, and thus set the
body's defense for ces in motion.
Certainly, not every for eign sub stance that enters the
body is treat ed as an enemy. Substances with for eign
prop er ties enter the body every time we eat, take med i ci -
nes or drink water. Yet our bod ies do not declare war on
these sub stan ces. In order for the defense cells to regard
a for eign sub stance as hos tile, cer tain con di tions must be
ful filled: such as the size of the "for eign" mol e cule, the
speed of expul sion from the body, and the way it
entered. 60
T cells play the main role in the immune sys tem's
fight against virus es and other microbes. T cells begin
their life in the bone mar row. After receiv ing an enemy
warn ing, imma ture ones head for the thy mus gland to
acquire more expert ise. In order for T cells to be use ful,
they need to be added by means of recep tors to the anti -
bod ies tar get ed against spe cif ic microbes.
Cells in the immune sys tem such as T cells use rec og -
ni tion pro teins like molec u lar flags and sign posts to
deter mine wheth er a cell belongs to the body. These pro -

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