Acquired Defects
Protein-calorie malnutrition is the leading cause of immune deficiency in the world. Protein-calorie malnutrition leads principally to a profound deficiency in the production and function of T cells, rendering the victim susceptible to many of the opportunistic infections that occur in genetic T cell deficiencies. With increasing protein-energy deficiency other parts of the immune system are also affected. Specific nutrient deficits such as iron or vitamin A deficiency also depress certain parts of the immune system.
Certain types of infections temporarily depress parts of the immune system. For example, many acute viral infections suppress cellular immunity for several days to a few weeks, and serious bacterial infections inhibit the ability of neutrophils to respond to chemotactic agents. Furthermore in schistosomiasis, Th1 responses are accentuated and Th2 responses are suppressed. This leads to a decreased ability to form antibodies after antigenic challenges.
Malnutrition and infection interact to inhibit the immune system. As a result of malnutrition, the immune system becomes compromised. That leads to respiratory and gastrointestinal infections. Those infections may in turn further interfere with the immune system. Moreover, some infections further compromise nutritional status by increasing nutrient losses (intestinal malabsorption) and utilization (fever, caloric expenditure during sweating) or by interfering with normal nutrient metabolic pathways (cachectic effect of TNF-α). Consequently, immune function is further impaired.
Certain types of infections temporarily depress parts of the immune system. For example, many acute viral infections suppress cellular immunity for several days to a few weeks, and serious bacterial infections inhibit the ability of neutrophils to respond to chemotactic agents. Furthermore in schistosomiasis, Th1 responses are accentuated and Th2 responses are suppressed. This leads to a decreased ability to form antibodies after antigenic challenges.
Malnutrition and infection interact to inhibit the immune system. As a result of malnutrition, the immune system becomes compromised. That leads to respiratory and gastrointestinal infections. Those infections may in turn further interfere with the immune system. Moreover, some infections further compromise nutritional status by increasing nutrient losses (intestinal malabsorption) and utilization (fever, caloric expenditure during sweating) or by interfering with normal nutrient metabolic pathways (cachectic effect of TNF-α). Consequently, immune function is further impaired.
A second acquired immunodeficiency is due to human immunodeficiency virus (HIV) infection. This retrovirus infection was first encountered in homosexual males and individuals who were injecting illicit drugs or who received blood products contaminated with the virus. The infection has since spread to heterosexual populations by sexual transmission. The infection has reached epidemic proportions in developed as well as developing countries and continues to increase. The resultant acquired immune deficiency syndrome (AIDS) occurs because the virus infects and destroys CD4+ T cells. The virus binds to the CD4 surface antigen on T cells and to the same or similar moiety on macrophages. Since CD4+ T cells are essential for the genesis of cellular immunity and for orchestrating the function of many other parts of the immune system, a deficiency in these T cells increases the patient's susceptibility to opportunistic infections. The vast majority of such infected patients die after several years. No preventative immunizations or curative treatments are available for the infection at this time.