“Immunodeficiency disorders are a group of disorders in which part of the immune system is missing or defective. Therefore, the body’s ability to fight infections is impaired. As a result, the person with an immunodeficiency disorder will have frequent infections that are generally more severe and last longer than usual.”

My definition of immunity is little different. There are no enemies. There is no war here. I consider ability of body to recognize self from non-self as immunity. And that part of body which shows non-self tendency (due to regular cell death or cancer or sudden collapse due to stress) is cleaned by immunity handlers.

Immunological-deficiency syndromes were not observed before 1952.

Yes, please note the year: 1952. 1950s. Post world war II. Era of wonder drugs i.e. antibiotics. Era of green revolution i.e. War weapon chemicals as fertilizers!