Hormones affect both men and women at the cellular and molecular level, and in general, the change of these individual hormones decrease optimal immune responses in both sexes. But there are sexual dimorphisms — differences between male and female — regarding the response to infection, and not just when we become senior citizens.

For example, sexually transmitted diseases occur more frequently and severely in women during their reproductive years due to behavior and sex-related mechanisms of reproduction but probably sex-specific steroid hormone levels as well.

At menopause, the amount of estrogen in women drops, enhancing the immunosenescent effects of age, and placing postmenopausal women at significant risk of infection. There are receptors for female hormones on most cells of the innate and adaptive immune system, including natural killer T cells, B cells, white cells called macrophages, and dendritic cells. This is at least part of the reason aging women lose their immunological advantage and face increased susceptibility and mortality regarding many infections like hepatitis, meningitis, and pneumonia.

Women also have more CD4 positive T cells and higher levels of the circulating antibodies, in particular IgM, which probably adds to a woman’s risk of autoimmune disease with age.

The effects of aging on men, however, can be just as startling, reflecting the lower levels of testosterone. Men experience a loss of energy, a mellowing of personality, and more risks for heart disease, hypertension, and stroke.

Age-related changes in the immune system also occur more rapidly in men. Male hormone receptors have been identified on both T and B lymphocytes, and studies show age-related changes in lymphocyte subsets in elderly men, with the decline of T cells (including naïve CD4, CD8, CD28, B cells), T cell proliferative capacity, and cytokine IL-6 secretion.

Certain cytokines are also decreased in men as they age, but not women. I suspect that the shorter life spans of men are related to these immune changes.