Lymphocytes Lymphocytes The immune system consists of cellular components and molecular components that work together to destroy antigens. (See also Overview of the Immune System.) Although some antigens (Ags) can... read more are components of the cellular immune system and include T cells, B cells,and natural killer (NK) cells, all of which are present in the peripheral blood; about 75% of the lymphocytes are T cells, 20% B cells, and 5% NK cells. Because lymphocytes account for only 20 to 40% of the total white blood cell (WBC) count, lymphocytopenia may go unnoticed when the WBC count is checked without a differential.
The normal lymphocyte count in adults is 1000 to 4800/mcL (1 to 4.8 × 109/L; in children < 2 years, the normal count is 3000 to 9500/mcL (3 to 9.5 × 109/L). At age 6 years, the lower limit of normal is 1500/mcL (1.5 × 109/L). Different laboratories may have slightly different normal values.
Almost 65% of blood T cells are CD4+ (helper) T cells. Thus, most patients with lymphocytopenia have a reduced absolute number of T cells, particularly in the number of CD4+ T cells. The average number of CD4+ T cells in adult blood is 1100/mcL (range, 300 to 1300/mcL [1.1 × 109/L with a range of 0.3 to 1.3 × 109/L]), and the average number of cells of the other major T-cell subgroup, CD8+ (suppressor) T cells, is 600/mcL (range, 100 to 900/mcL).
Deficiencies of particular subsets of lymphocytes (eg, CD4+, CD8+, B, NK cells) may not be reflected in the lymphocyte count in the blood but may result in a functional lymphocytopenia. It is also important to note that the lymphocytes in the blood represent only a small proportion of the total lymphocyte pool and may not always correlate with the composition and numbers of lymphocytes in other lymphoid (eg, nodes, spleen) and non-lymphoid (eg, lung, liver) tissues.
Lymphocytopenia can be
Acquired lymphocytopenia can occur with a number of other disorders (see table Causes of Lymphocytopenia Causes of Lymphocytopenia Lymphocytopenia is a total lymphocyte count of 1000/mcL ( 1 × 109/L) in adults or 3000/mcL ( 3 × 109/L) in children 2 years. Sequelae include opportunistic infections and an increased risk of... read more ).
The most common causes include
Protein-energy undernutrition is the most common cause worldwide.
AIDS Human Immunodeficiency Virus (HIV) Infection Human immunodeficiency virus (HIV) infection results from 1 of 2 similar retroviruses (HIV-1 and HIV-2) that destroy CD4+ lymphocytes and impair cell-mediated immunity, increasing risk of certain... read more patients routinely have lymphocytopenia, which arises from destruction of CD4+ T cells infected with HIV. Lymphocytopenia may also reflect impaired lymphocyte production arising from destruction of thymic or lymphoid architecture. In acute viremia due to HIV or other viruses, lymphocytes may undergo accelerated destruction from active infections with the virus, may be trapped in the spleen or lymph nodes, or may migrate to the respiratory tract.
Patients with COVID-19 COVID-19 Coronaviruses are enveloped RNA viruses that cause respiratory illnesses of varying severity from the common cold to fatal pneumonia. Numerous coronaviruses, first discovered in domestic poultry... read more also frequently have lymphocytopenia (35 to 83% of patients). Lower lymphocyte counts portend a poor prognosis and an increased likelihood of requiring ICU admission and of dying from the disease. The cause of the lymphocytopenia is not completely understood, but COVID-19 can directly infect lymphocytes, and a cytokine-related apoptosis of the cells is likely.
Iatrogenic lymphocytopenia is caused by cytotoxic chemotherapy, radiation therapy, or the administration of antilymphocyte globulin (or other lymphocyte antibodies). Long-term treatment for psoriasis using psoralen and ultraviolet A irradiation may destroy T cells. Long-term glucocorticoid therapy can induce lymphocyte destruction.
Lymphocytopenia may occur with lymphomas Overview of Lymphoma Lymphomas are a heterogeneous group of tumors arising in the reticuloendothelial and lymphatic systems. The major types are Hodgkin lymphoma and non-Hodgkin lymphoma (see table Comparison of... read more , autoimmune diseases such as systemic lupus erythematosus Systemic Lupus Erythematosus (SLE) Systemic lupus erythematosus is a chronic, multisystem, inflammatory disorder of autoimmune etiology, occurring predominantly in young women. Common manifestations may include arthralgias and... read more , rheumatoid arthritis Rheumatoid Arthritis (RA) Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease that primarily involves the joints. RA causes damage mediated by cytokines, chemokines, and metalloproteases. Characteristically... read more , or myasthenia gravis Myasthenia Gravis Myasthenia gravis involves episodic muscle weakness and easy fatigability caused by autoantibody- and cell-mediated destruction of acetylcholine receptors. It is more common among young women... read more , and protein-losing enteropathy caused by gastrointestinal disease or constrictive pericarditis.
Inherited lymphocytopenia (see table Causes of Lymphocytopenia Causes of Lymphocytopenia Lymphocytopenia is a total lymphocyte count of 1000/mcL ( 1 × 109/L) in adults or 3000/mcL ( 3 × 109/L) in children 2 years. Sequelae include opportunistic infections and an increased risk of... read more ) most commonly occurs in
It may occur with inherited immunodeficiency disorders Overview of Immunodeficiency Disorders Immunodeficiency disorders are associated with or predispose patients to various complications, including infections, autoimmune disorders, and lymphomas and other cancers. Primary immunodeficiencies... read more and disorders that involve impaired lymphocyte production. Other inherited disorders, such as Wiskott-Aldrich syndrome Wiskott-Aldrich Syndrome Wiskott-Aldrich syndrome results from a combined B- and T-cell defect and is characterized by recurrent infection, eczema, and thrombocytopenia. (See also Overview of Immunodeficiency Disorders... read more , adenosine deaminase deficiency Adenosine deaminase deficiency Purines are key components of cellular energy systems (eg, ATP, NAD), signaling (eg, GTP, cAMP, cGMP), and, along with pyrimidines, RNA and DNA production. Purines and pyrimidines may be synthesized... read more , and purine nucleoside phosphorylase deficiency Purine nucleoside phosphorylase deficiency Purines are key components of cellular energy systems (eg, ATP, NAD), signaling (eg, GTP, cAMP, cGMP), and, along with pyrimidines, RNA and DNA production. Purines and pyrimidines may be synthesized... read more , may involve accelerated T-cell destruction. In many disorders, antibody production is also deficient.
Lymphocytopenia per se generally causes no symptoms. However, findings of an associated disorder may include
Absent or diminished tonsils or lymph nodes, indicative of cellular immunodeficiency
Skin abnormalities (eg, alopecia, eczema, pyoderma, telangiectasia)
Evidence of hematologic disease (eg, pallor, petechiae, jaundice, mouth ulcers)
Generalized lymphadenopathy and splenomegaly, which may suggest HIV infection Symptoms and Signs Human immunodeficiency virus (HIV) infection results from 1 of 2 similar retroviruses (HIV-1 and HIV-2) that destroy CD4+ lymphocytes and impair cell-mediated immunity, increasing risk of certain... read more or Hodgkin lymphoma Hodgkin Lymphoma Hodgkin lymphoma is a localized or disseminated malignant proliferation of cells of the lymphoreticular system, primarily involving lymph node tissue, spleen, liver, and bone marrow. Symptoms... read more
Patients with lymphocytopenia experience recurrent infections or develop infections with unusual organisms. Pneumocystis jirovecii Pneumocystis jirovecii Pneumonia Pneumocystis jirovecii is a common cause of pneumonia in immunosuppressed patients, especially in those infected with human immunodeficiency virus (HIV) and in those receiving systemic corticosteroids... read more , cytomegalovirus Cytomegalovirus (CMV) Infection Cytomegalovirus (CMV, human herpesvirus type 5) can cause infections that have a wide range of severity. A syndrome of infectious mononucleosis that lacks severe pharyngitis is common. Severe... read more , rubeola Measles Measles is a highly contagious viral infection that is most common among children. It is characterized by fever, cough, coryza, conjunctivitis, an enanthem (Koplik spots) on the oral mucosa... read more , and varicella Chickenpox Chickenpox is an acute, systemic, usually childhood infection caused by the varicella-zoster virus (human herpesvirus type 3). It usually begins with mild constitutional symptoms that are followed... read more pneumonias often are fatal. Lymphocytopenia is also a risk factor for the development of cancers and for autoimmune disorders.
Lymphocytopenia is suspected in patients with recurrent viral, fungal, or parasitic infections but is usually detected incidentally on a CBC. P. jirovecii, cytomegalovirus, rubeola, or varicella pneumonias with lymphocytopenia suggest immunodeficiency.
Lymphocyte subpopulations are measured in patients with lymphocytopenia. Measurement of immunoglobulin levels should also be done to evaluate antibody production. Patients with a history of recurrent infections undergo complete laboratory evaluation for immunodeficiency Approach to the Patient With Suspected Immunodeficiency Immunodeficiency typically manifests as recurrent infections. However, recurrent infections are more likely to have causes other than immunodeficiency (eg, inadequate treatment, resistant organisms... read more , even if initial screening tests are normal.
In acquired lymphocytopenias, lymphocytopenia usually remits with removal of the underlying factor or successful treatment of the underlying disorder. IV or subcutaneous immune globulin is indicated if patients have chronic immunoglobulin G deficiency, lymphocytopenia, and recurrent infections. Hematopoietic stem cell transplantation Hematopoietic Stem Cell Transplantation Hematopoietic stem cell (HSC) transplantation is a rapidly evolving technique that offers a potential cure for hematologic cancers (leukemias, lymphomas, myeloma) and other hematologic disorders... read more can be considered for all patients with congenital immunodeficiencies and may be curative.
Avoid giving live vaccines (because of the risk of causing infection) in these patients. Inactive or recombinant vaccines are safe, but their efficacy is variable depending on type and severity of the lymphocytopenia.
Lymphocytopenia is most often due to AIDS, and recently COVID-19, or undernutrition, but it also may be inherited or caused by various infections, drugs, or autoimmune disorders.
Patients have recurrent viral, fungal, or parasitic infections.
Lymphocyte subpopulations and immunoglobulin levels should be measured.
Treatment is usually directed at the cause, but occasionally, IV or subcutaneous immune globulin or, in patients with congenital immunodeficiency, stem cell transplantation is helpful.
Avoid giving live vaccines in these patients.
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