Definition and Overview
The immune system is the body’s natural defense mechanism. It serves to protect the body from infections and diseases. A complex interaction of the various components of this system, which includes B cells and T cells, produces the immune response.
Immunodeficiency is a general term referring to the state wherein the ability of the body’s immune system to ward off diseases and infections is compromised or weakened. Thus, immunodeficient patients become susceptible to developing various infections or malignancies.
Immunodeficiency syndromes may be broadly categorized based on the affected component of the immune system. Abnormalities in B cells result in defective humoral immunity. This kind of immunodeficiency leads to hypogammaglobulinemia (a decrease in antibodies) or agammaglobulinemia (absence of antibodies). Meanwhile, abnormalities in T cells result in defective cell-mediated immunity, predisposing the individual to viral infections. This kind of immunodeficiency is typically associated with secondary immunodeficiency syndromes. Severe combined immunodeficiency, or SCID, is the most severe and fatal type of immunodeficiency. With SCID, both B and T cell functions are affected, making the patient susceptible to all kinds of infections. Other components of the immune system, such as granulocytes and the complement system, may likewise be affected in immunodeficiency syndromes, albeit less commonly.
Immunodeficiency disorders can range from a mild condition causing recurrent minor illnesses to a severe, life-threatening disease. Mild immunodeficiency disorders are fairly common, occurring in about 1 in every 600 persons in the US and Europe. The more severe kinds, however, are generally rare and are usually fatal particularly during childhood.
Cause of Condition
Immunodeficiency may be primary or secondary. Primary immunodeficiency is a congenital disorder; this means that the disorder has been present since birth and may have been inherited. In primary immunodeficiency, genetics play a major role. Patients with this kind of immunodeficiency are born with defects in specific components of their immune system. More than 80 kinds of primary immunodeficiencies have been identified.
Secondary immunodeficiency, meanwhile, is acquired. A variety of external factors contribute to the development of this condition including old age and malnutrition. Diseases that can cause immunodeficiency are chronic infections, disseminated tuberculosis, acquired immune deficiency syndrome (AIDS) and cancer, specifically malignancies of the blood cell lines and the bone marrow. Splenectomy, the surgical removal of the spleen for any reason, may also produce immunodeficiency syndromes. Aside from these, certain medications may alter the function of the immune system, resulting in immunosuppression. These medications include chemotherapeutic drugs, transplant medications, and steroids, among others. Secondary immunodeficiencies are more commonly encountered than primary immunodeficiencies.
The major symptom of immunodeficiency syndromes is an increased susceptibility to infections. Patients with defective humoral immunity are predisposed to infections by bacteria. Patients with this kind of immunodeficiency experience recurrent bouts of respiratory infections, including pneumonia, gastrointestinal infections, and meningitis. Chronic infections, such as otitis media, can also occur. Patients who have agammaglobulinemia tend to develop severe infections, usually leading to a fatal course.
On the other hand, patients with defective cell-mediated immunity are susceptible to infections by viruses and fungi. In these patients, infection with viruses that are generally latent, such as Varicella zoster and Herpes simplex, can be disseminated. Fungal infections also tend to become systemic. Candidiasis or yeast infection is common, usually affecting the mucous membranes.
The immune response involves interactions between the B and T cells; because of this, there is usually an overlap in the symptoms of patients. Therefore, patients who have humoral immunodeficiency may also develop recurrent and chronic viral infections, while patients who have cell-mediated immunodeficiency are also prone to developing pyogenic bacterial infections. Patients with severe combined immunodeficiency typically develop multiple, simultaneous infections.
Who to See and Types of Treatments Available
Individuals who experience recurrent infections, especially when severe, need to consult a general practitioner immediately. These patients will have to undergo a number of laboratory examinations to aid both diagnosis and treatment. Patients with immunodeficiencies are typically referred to a hematologist, a specialist in managing blood disorders. Those with ongoing infections may also be referred to an infectious disease specialist.
The treatment of primary immunodeficiency disorders is directed towards the management of ongoing infections and prevention of the development of further infections and diseases. Patients with ongoing infections are managed aggressively. They are typically given broad-spectrum antibiotics over a long period of time. Antiviral and anti-fungal medications are also given when needed. Prophylactic or preventive treatment with medications may also be considered.
Patients with humoral immunodeficiency, on the other hand, may have to undergo replacement therapy, which involves the administration of human immunoglobulin every 4 weeks via the intravenous route to maintain specific levels of antibodies in the body. Replacement therapy must be done with medical supervision, as an infusion of immunoglobulins can have serious side effects. When given adequate replacement therapy, patients with B cell immunodeficiency can lead generally healthy, productive lives.
Bone marrow transplantation can be used to treat certain kinds of immunodeficiency disorders. Novel therapeutic options, such as stem cell transplantation, may also be considered for immunodeficient patients. Researches on gene therapy can help improve the understanding of these conditions and will hopefully aid in developing future treatment strategies for these patients.
Secondary immunodeficiency disorders are treated by modifying the external factors causing the condition. Decreasing the dosage of or completely replacing medications causing immunosuppression, such as steroids, may be necessary. Individuals undergoing elective splenectomy need to be vaccinated prior to the procedure. HIV patients need to be given antiretroviral drugs to control the virus and strengthen their immune system.
Patients with weak immune systems are advised to avoid or minimize contact with individuals who have infections. Protective gear, such as a facemask, is likewise recommended, especially when going out in public. Blood transfusions and the administration of live vaccines should also be avoided in patients with T-cell deficiency and SCID, as these may cause graft-versus-host disease or deadly infections.
- Ballow M. Primary immunodeficiency diseases. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 258.