Immune System Aging in a Nutshell
A review paper: "With the improvement of medical care and hygienic conditions, there has been a tremendous increment in human lifespan. However, many of the elderly (older than 65 years) display chronic illnesses, and a majority requires frequent and longer hospitalization. The robustness of the immune system to eliminate or control infections is often eroded with advancing age. Nevertheless, some elderly individuals do cope better than others. The origin of these inter-individual differences may come from genetic, lifestyle conditions (nutrition, socio-economic parameters), as well as the type, number and recurrence of pathogens encountered during life. The theory we are supporting is that chronic infections, through life, will induce profound changes in the immune system probably due to unbalanced inflammatory profiles. Persistent viruses such as cytomegalovirus are not eliminated and are a driven force to immune exhaustion. Because of their age, elderly individuals may have seen more of these chronic stimulators and have experienced more reactivation episodes ultimately leading to shrinkage of their repertoire and overall immune robustness." Evidence in recent years suggests that this issue can be addressed by selectively destroying immune cells devoted to largely useless causes such cytomegalovirus - a goal that becomes ever more practical as targeted cell-killing therapies move closer to the clinic.
Once the majority of the immune systems cells reach their Hayflick limit there simply is not enough robust protection left to take on the invading pathogens or the "bad" copy cancer cells of internal origin. The line of defense is overwhelmed and the pathogens run amuck.
During the Civil War President Lincoln would dutifully visit the wounded at the US Soldiers home. Once his famous top hat came off while riding up to the grounds. When it was retrieved they found a bullet hole in it. The Soldiers home was protected by retired veterans and those unable to return to the field of battle. Later a brazen band of Confederate Calvary crossed the Potomac South of Frederick, Md. and proceeded to raid their way to Silver Spring which borders the District of Columbia. They found little resistance and were proceeding into the nerve center of the Union. Fortunately there were experienced Union Soldiers landing near Georgetown that were quickly deployed to drive the raiders back or we might have a different conclusion to the story of our history.
Simply removing unnecessary combatants will not solve the problem. Strong and able replicants are required to maintain and heal the host. Telomerase activation is the most promising method of extending the life of the stem cells, immune cells etc. to not only keep the "host" alive but to allow the expression of the human spirit toward the pursuit of happiness indeed.