The following is a great overview of immune system involvement in Alzheimers. I am a follower of the concept that the robust immune system that evolved to protect us when we are young becomes overactive and off target when we grow old, and montelukast and other leukotriene blocking drugs can reduce the overactivation of the immune system in middle and old age.

https://www.npr.org/sections/health-shots/2022/01/30/1076166807/how-a-hyperactive-cell-in-the-brain-might-trigger-alzheimers-disease

Interesting 

I noticed my immune system is not as good as it used to be. I’m getting sick more often.

I’m down with a stomach virus for over a week.