Page 92 - The Miracle in the Immune System

90 THE MIRACLE OF THE IMMUNE SYSTEM

The ability of the helper T cell to produce a mole-
cule, which activates another cell, is a very important
process.
First, the production of this molecule is related to
an impending war strategy. It is obvious that the cells
cannot make up this strategy themselves, nor can the
strategy come about by sheer coincidence.
Developing a strategy would not be enough either.
The molecule in the cell, which will switch on the pro-
duction key in the other cell, should be synthesised ac-
curately. For this, it has to be perfectly aware of the
chemical structure of the opposite cell.
A mistake made in the production of this molecule
alone would paralyze the defence system entirely. This

How do Helper-T cells start action?

Microscopic Antigen complex
pieces
Helper-T (CD4) cell

Antigen
Antigen
containing cell
Receptor
CD4

Microbe

The picture illustrates how a cell breaks a microbe apart and
presents it to the T cell. As the picture at the right indicates,
the T cell will be activated only if its antigen receptor fits to the
presented antigen, if the CD4 molecule adheres to the antigen
complex, and if some other molecules (right) combine with
each other. These safety mechanisms prevent a mature T cell
from moounting an immune attack against its host.