Peacekeeper cells protect the body from autoimmunity during infection | Biological Sciences Division | The University of Chicago
A significant issue with our immune system is that it is poorly "designed." If it were truly the product of an intelligent designer, as creationists claim, that designer would hardly be competent enough to design a simple household item, let alone a complex biological system.
Because our immune system is so disorganized and inefficient, multiple layers of complexity have evolved to mitigate its worst shortcomings. However, these added layers themselves remain prone to errors, as they reflect the same flawed foundation. The central problem arises because the immune system must balance two contradictory requirements: it needs to be sensitive enough to identify and eliminate genuine threats, yet not so sensitive that it mistakenly attacks the body's own tissues.
While an omnipotent, supremely intelligent designer should have easily resolved such a contradiction, the reality is that our immune system frequently fails on both counts. It often permits pathogens and parasites to invade, and it also frequently turns against the body itself, leading to autoimmune diseases such as lupus, diabetes, multiple sclerosis, arthritis, and kidney or liver failure, among numerous other debilitating conditions that cause immense suffering.
Like the whimsical contraptions created by cartoonist William Heath Robinson — complex machines built from objects originally intended for entirely different purposes - the mammalian immune system is not designed top-down from a clear blueprint. Rather, it's built up gradually from one makeshift adaptation piled onto another, each new solution attempting to compensate for the shortcomings of earlier ones. Eventually, this process results in a ramshackle system so intricate that its complexity itself creates new opportunities for failure. Such complexity is not indicative of intelligent, purposeful design, which would typically favour simplicity and efficiency. Instead, it reflects an ad hoc, utilitarian approach driven by evolutionary constraints and an inability to anticipate future challenges.
And of course, this embarrassment for creationism is made worse by the fact that, according to Michael J. Behe, pathogenic parasites such as E. coli and Plasmodium falciparum are examples of irreducible complexity, so are, in creationist circles, unarguable 'proof' of intelligent design, so the immune system is allegedly designed by the designer of these pathogens to protect us from them.
It seems creationists have no difficulty in believing the same designer would design parasites to make sick, then design a system to protect us from its pathogenic designs, and even though that system doesn't work very well, it is nevertheless evidence of supreme intelligence.