There is a general slowing the process of cell division with aging, no matter what tissue is examined. Secondly, every human experiences a gradual shrinking of the thymus gland with age. As a result, thymic influences on the production and maturation of all classes of -cells is reduced. The end result of these changes in immune function is an age-related increase in the vulnerability to infectious disease and cancer. Removal of drugs should result in a return to normal conditions.
Nutritional deficiencies can also cause immune compromise.
Socioeconomic factors can lend to both vitamin B12 and folate deficiencies. Folate is found in green leafy vegetables and B12 is problematic due to gastric atrophy in aging. Alcoholism can make things worse for both. The following list provides the most common syndromes. Cause is varied.