(Selected Tables and Figures referenced, but not present in this blog
can be found in their corresponding Science Version blogs)
We spoke in the last blog about how, over hundreds of millions of years, the immune system became capable of identifying virtually any foreign, antigen that might attack us. That sounds incredible when you think of the trillions of antigens we have mentioned in previous blogs. But, I guess over hundreds of millions of years, good old Darwinian natural selection put us in a pretty good place relative to our environment. (Remember Einstein's saying, “The environment is everything that isn’t me.” Well, evolution created this amazing system of immunity through the development of something called “antibody-encoding genes” which can identify (code for) any antigen. Its discovery won a Nobel Prize in 1987).
Since the immune system is pivotal in human survival, its evolution had to create protection for all the body’s systems and it did so through a process referred to as the “allocation rule of the life-history theory.” The body’s systems require energy to function and this evolutionary process used natural selection (there it is again) to create a strategy wherein the immune system proportions or “allocates” its energy to individual body functions and stores the excess energy for other body functions if and when needed. Kind of a “rainy day” system of protection. All pretty amazing stuff and it tells us that the immune system is still evolving and hopefully, will provide future protection against diseases and, even aging.
It seems that women have evolutionary bias towards producing more immune B cells that produce antibodies which is good news…and bad (more immune paradoxes). It certainly adds protection against those nasty pathogens, but too many antibodies or “too much self” can also begin to convert into autoantibodies and produce autoimmune reactions and disease. But evolution also used this increased B cell generation in females to allow better maternal protection for her offspring. So it seems that evolution promotes protect against infection regardless of the cost as in the offspring example in women. On the other hand, men have evolved with more T cells which protects them, a little at least, from those autoimmune disease of which women suffer more.
Immune memory is another important trait that improves human protection against reinfection. This memory function exists in both the passive innate immune system as well as the more aggressive adaptive immune system which we’ll be describing in Blog #9. The innate immune memory is more non-specific and can’t really adapt to variants in antigens. It uses mostly T cell memory and is called “primed or trained immunity.” The adaptive immune system, on the other hand, evolved later than the innate form and has the capability to recognize different antigens and pathogens by using combinations of antibodies and those B cell antibody-encoding genes mentioned above, to build a more diversified memory capability. Remembering that females have more B cells, the increased level of B-cells and resultant B-memory cells may also contribute to increased adaptive immune memory in females. Yet another female bias.
Finally, that adaptive immunity that we’re building up to in Blog #9, evolved the ability to diversify its antigen receptor genes, those receptors on the lymphocyte cells that recognize antigens. This enables these specialized cells to produce antibodies with greater binding power to antigens. At birth, females activate these stronger cell-binding powers while it takes males as long as 36 months to acquire similar cellular capabilities. Thus, once again, females demonstrate stronger immune systems as compared to the immature male system even as early as birth. And introducing natural selection one more time, these differences between a stronger immune system in females persist over time leading to the female having greater protection against infectious disease than the male.
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