For example, Bruton's Hypogammagloulinemia is an X linked genetic disorder resulting in a deficiency of B cells. Gender plays a role. Temperature is a factor. Lymphocytes perform best at 40 degrees centigrade. Sleep wake cycles play a role.
Sleep deprivation decreases the ability of neutrophils to phagocytize.
Cortisol, produced in greatest amounts at 5AM suppresses immune functioning. Nutrition plays a role, both malnutrition and obesity increases the incidence of infectious diseases. Clinically The treatment for refractory leukemia is a bone marrow transplant. Because the leukemic cells reside in the bone marrow, total irradiation of the bone marrow is done in order to fully destroy all the leukemic cells. Of course, total irradiation also kills the normal elements including the plurioptential stem cells.