Immunosenescence - the decline of our immune system as we grow old

(First of two parts)

Nature has not meant for us to grow old. Nature simply wants us to reproduce ourselves; afterwards, she causes us to rapidly deteriorate. As we age, we are no longer able to run as fast as when we were young, we get tired more easily, it takes longer for our wounds to heal, etc. (many of those who are reading this are probably all too familiar with the aches and pains associated with growing old). If we were still living in the jungle, with predators all around us, those of us who are old would soon be “recycled.” Nature’s goal is the perpetuation of the species, so that resources, if limited, are saved for those who can contribute more toward the fulfillment of that goal. Nature has caused us (and other organisms) to be born with the conviction that those who compete for limited resources are best eliminated; alliances with those who enhance access to those resources are best formed. We apply the notion of competition and alliance not only to other species, but also to members of our own species. By Nature’s reckoning, the old, who are no longer able to contribute significantly to the welfare of the species and who now pose competition for resources, are best eliminated. Nature is so unfeeling. 

But we defy Nature and we have developed means that allow us to grow old. We no longer fear the predators that used to chase us, hoping to feast on our flesh (we have killed most of them off). We have developed drugs that fight many of the parasites that plague us (but there are still very many that we have to get rid of, or at least control). We have developed mechanical means to allow the incapacitated to walk and even to run. We have developed electrical means to allow even the severely hearing impaired to hear. Indeed, more and more, we can grow very old despite Nature. (And we have learned to cherish the old — many of us, anyway.)

Ah, but Nature still has a few tricks up her sleeve.

Nature has provided us with the means to ward off disease, to fight organisms that cause disease. Our skin is a barrier that prevents entry of parasites and pathogens. The acid in our stomach usually can kill organisms that get in by way of our mouth. The tears in our eyes, the saliva in our mouth, and other secretions protect our other orifices. If viruses, bacteria, fungi, and other pathogens manage to get past those barriers, they will still have to contend with our immune system. 

Our immune system is our ultimate protection against disease. We have cells and molecules that are specially designed to recognize substances that do not belong in our body. Immune cells and molecules patrol our organs and tissues, seeking out foreign substances. Germs and other pathogens are killed and the harmful molecules that they produce are neutralized and expelled from our body. Our immune system also gets rid of our own cells that have become abnormal, or are no longer functioning properly.

Very importantly, our immune system produces “memory cells” that remember previous encounters with a pathogen, so that the immune reaction to any new invasion is much faster. Immune memory is the rationale for vaccination — and for its success. Memory cells have been found to persist for more than 50 years in individuals who had been vaccinated against smallpox and for more than 90 years in survivors of the 1918 flu pandemic. Clearly, immune memory persists for many years and sometimes for a lifetime.

So, what does Nature do? To prevent us from getting (too) old, Nature weakens our immune system as we age — a condition called “immunosenescence” (immune aging). With the decline of our immune system, we more easily succumb to infection, we are more prone to cancer, we are more susceptible to seasonal diseases like the flu, etc., and vaccination, which we have invented to protect us from many diseases, becomes less and less effective.

For example, there were reports several years ago (in 2005 and 2006) of studies that showed that vaccination against flu of people 65 years old and older was not significantly protective. That finding was bolstered by a more recent finding (last year) that vaccination against flu of people over 70 years old did not reduce mortality. From these findings, it would seem that vaccination of the elderly is a waste. That is frightening, since 90 percent of flu deaths are of elderly individuals (who are more susceptible to pneumonia and other complications of flu).

Can we defy Nature one more time? 

(To be concluded)

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Eduardo A. Padlan is a corresponding member of the NAST and is an adjunct professor in the Marine Science Institute, College of Science, University of the Philippines Diliman. He can be reached at [email protected].