The immune system is divided into two categories of cells: those of the innate and acquired immunity from those.
Innate immunity is a crude and ineffective response against bacteria. It is provided primarily by cells "generic" in the sense that they are all identical in our bodies, and represent (slightly) the largest population of circulating immune cells. These are the neutrophils (the little soldiers).
The second
immunity, acquired, is an evolutionary innovation in vertebrates. It is much more complex and far more effective because it gives an appropriate response to the infectious agent. In this
immunity, many different cell types together, but most important of them has absolutely no effect on bacteria and viruses.
These are called helper T cells. Their role is coordinating the response by transmitting activation signals and suppression of other cells that will act on the infectious agent. Their role is to communicate, massively.
Even if they are less likely to move as neutrophils (toy soldiers), they cost much more to the organization: their genetic material is heavier, and their production and very long because it requires a huge "reflection" biological mechanisms internal selection (only 2% of them around), and a dedicated body, thymus.
Communication and information are the cornerstones of immunity.
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