Idiopathic CD4 positive T-lymphocytopenia (ICL) is a rare disorder of the immune system. People with ICL have low levels of a type of white blood cell, called a CD4+ T cell. These low levels can not be explained by other causes of immunodeficiency, including HIV infection. T cells have many jobs in our immune system, such as attacking bacteria and viruses. CD4 is a protein found on the surface of many different cells within your immune system. It lets the different cells of your immune system work with each other. When CD4+ T cells are decreased, your body becomes more prone to infection.

Signs and Symptoms of ICL vary. Some people have no symptoms, however most have illnesses suggestive of a lowered immune system, including infections (varicella-zoster virus, human papilloma virus), autoimmune disorders (autoimmune hemolytic anemia, lupus), and certain types of cancer (non-Hodgkin lymphoma). A few people with ICL are found to carry specific genemutations; however, for most cases of ICL the underlying cause is not known. Currently, there is no cure for ICL, but treatments are available to help manage individual symptoms.

• Bacterial:Mycobacterium, Salmonella, Nocardia
• Fungal:Candidiasis, Cryptococcus, Histoplasmosis
• Viral: Cytomegalovirus, varicella zoster virus, human papillomaviruses
• Parasitic: Toxoplasmosis, leishmaniasis

Autoimmune disorders including Sjögren syndrome, sarcoidosis, psoriasis, autoimmune hemolytic anemia, and lupus and malignancies (cancers) including squamous cell carcinoma, and lymphoma may also occur.

The cause of ICL is not well understood. Contributing factors may be related to CD4+ T cell development and function, various deficiencies of the immune system, and genetic factors.

The following diseases may also cause decreased CD4+ T cell counts and could be considered as an alternative diagnosis: acute or chronic retroviral infections (HIV, human T-lymphotropic virus type 1), sarcoidosis, common variable immunodeficiency, congenital immunodeficiencies, and immunosuppressive states induced by chemotherapy, acute respiratory distress syndrome, or autoimmune disorders.

Two different methods to increase CD4+ T cell counts have been used on a few affected individuals with varying levels of success: Interleukin-2 (IL2) and bone marrow transplantation. IL2 is a type of protein naturally occurring in the immune system that works to increase the production and function of the immune system. A bone marrow transplant is a procedure to replace damaged or destroyed bone marrow (soft, fatty tissue inside your bones that produces blood cells) with healthy bone marrow stem cells. Stem cells are immature cells in the bone marrow that give rise to all of your different blood cells.

The long-term outlook (prognosis) for individuals with ICL varies depending on the extent of immunosuppression and the associated symptoms. Rarely, ICL can be a temporary finding that reverses over time. In most cases the level of CD4+ T cells stabilizes, rather than continuing to decrease.