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Unlike primary immunodeficiencies, which have a genetic basis, secondary immunodeficiencies are often reversible if the underlying cause is resolved. Patients with secondary immunodeficiencies develop an increased susceptibility to an otherwise benign infection by opportunistic pathogens such as Candida spp., P. jirovecii , and Cryptosporidium .
HIV infection and the associated acquired immunodeficiency syndrome (AIDS) are the best-known secondary immunodeficiencies. AIDS is characterized by profound CD4 T-cell lymphopenia (decrease in lymphocytes). The decrease in CD4 T cells is the result of various mechanisms, including HIV-induced pyroptosis (a type of apoptosis that stimulates an inflammatory response), viral cytopathic effect, and cytotoxicity to HIV-infected cells.
The most common cause of secondary immunodeficiency worldwide is severe malnutrition, which affects both innate and adaptive immunity. More research and information are needed for the more common causes of secondary immunodeficiency; however, the number of new discoveries in AIDS research far exceeds that of any other single cause of secondary immunodeficiency. AIDS research has paid off extremely well in terms of discoveries and treatments; increased research into the most common cause of immunodeficiency, malnutrition, would likely be as beneficial.
Benjamin, a 50-year-old male patient who has been receiving chemotherapy to treat his chronic myelogenous leukemia ( CML ), a disease characterized by massive overproduction of nonfunctional, malignant myelocytic leukocytes that crowd out other, healthy leukocytes, is seen in the emergency department. He is complaining of a productive, wet cough, dyspnea, and fatigue. On examination, his pulse is 120 beats per minute (bpm) (normal range is 60–100 bpm) and weak, and his blood pressure is 90/60 mm Hg (normal is 120/80 mm Hg). During auscultation, a distinct crackling can be heard in his lungs as he breathes, and his pulse-oximeter level (a measurement of blood-oxygen saturation) is 80% (normal is 95%–100%). He has a fever; his temperature is 38.9 °C (102 °F). Sputum cultures and blood samples are obtained and sent to the lab, but Benjamin goes into respiratory distress and dies before the results can be obtained.
Benjamin’s death was a result of a combination of his immune system being compromised by his leukemia and his chemotherapy treatment further weakening his ability to mount an immune response. CML (and leukemia in general) and corresponding chemotherapy cause a decrease in the number of leukocytes capable of normal function, leading to secondary immunodeficiency. This increases the risk for opportunistic bacterial, viral, protozoal, and fungal infections that could include Staphylococcus , enteroviruses, Pneumocystis , Giardia, or Candida . Benjamin’s symptoms were suggestive of bacterial pneumonia, but his leukemia and chemotherapy likely complicated and contributed to the severity of the pneumonia, resulting in his death. Because his leukemia was overproducing certain white blood cells, and those overproduced white blood cells were largely nonfunctional or abnormal in their function, he did not have the proper immune system blood cells to help him fight off the infection.
[link] summarizes primary and secondary immunodeficiencies, their effects on immune function, and typical outcomes.
| Primary and Secondary Immunodeficiencies | |||
|---|---|---|---|
| Disease | Effect on Immune Function | Outcomes | |
| Primary immunodeficiencies | Chronic granulomatous disease | Impaired killing of bacteria within the phagolysosome of neutrophils and macrophages | Chronic infections and granulomas |
| Selective IgA deficiency | Inability to produce secretory IgA | Predisposition to lung and gastrointestinal infections | |
| Severe combined immunodeficiency disease (SCID) | Deficient humoral and cell-mediated immune responses | Early development of severe and life-threatening opportunistic infections | |
| X-linked agammaglobulinemia | Flawed differentiation of B cells and absence of specific antibodies | Recurrent infections almost exclusively due to pathogens that cause pyogenic infections | |
| Secondary immunodeficiencies | Immunosuppressive therapies (e.g., chemotherapy, radiotherapy) | Impaired humoral and/or cell-mediated immune responses | Opportunistic infections, rare cancers |
| Malnutrition | Impaired humoral and/or cell-mediated immune responses | Opportunistic infections, rare cancers | |
| Viral infection (e.g., HIV) | Impaired cell-mediated immune responses due to CD4 T-cell lymphopenia | Opportunistic infections, rare cancers |
Diseases due to ________ abnormalities are termed primary immunodeficiencies.
genetic
A secondary immunodeficiency is ________, rather than genetic.
acquired
Compare the treatments for primary and secondary immunodeficiencies.
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