Cell surface marker expressed by class II CD4 restricted T cells and by natural killer T cells.

Positive T cell lymphocyte counts in the blood is an imperfect assessment of the body’s total reservoir of CD4+ T cells since on 1-2% of such cells are found in the peripheral blood.

As many as 30% of all T cells reside in the mucosa, mainly the gut.

Depletion of CD4 cells is a hallmark of progressive human immunodeficiency virus disease and a predictor of the short term risk of progression to AIDS.

CD4+ T cells central role in defense against pathogens by helping other cells to acquire and execute their effector functions.

Cells impede spread of viruses via secretion of cytokines such as gamma-interferon that block viral replication.

CD4-positive cells count remains the best single indicator of immunodeficiency related to infection with HIV.

Range defines conditions of HIV complications by stage of immunosuppression:

A normal CD4 cell count can range from 500/microL to 1500/microL.

>500 cells/ul-a normal range with no symptoms except during primary HIV infection.

350-500 cells/ul-usually no symptoms but may have a slight increased risk of tuberculosis and long periods of time in this range may modestly increases the risk of cancer and heart disease.

The best evidence of benefit from HIV anti-retro viral therapy is for people with a CD4 cell count below 350/µL.

200-350 cells/ul-increased risk of shingles, bacterial pneumonia, oral and vaginal candidiasis, fatigue, oral hairy leukoplakia, tuberculosis Kaposi’s sarcoma and Mycobacterium infections.

100-200 cells/ul-cervical cancer, lymphomas, pseudocysts carinii pneumonia, toxoplasmosis, coccidioidomycosis, histoplasmosis and recurrent pneumonia.

<100 cells/ul-esophageal and bronchial candidiasis, cryptosporidiosis, Cytomegalovirus infections, herpes simplex, CNS lymphoma mycobacterium infections and progressive multifocal leukoencephalopathy.

After HIV-1 infection begins a transient, spontaneous restoration of CD4 positive T-cell counts occurs in the four-month time window and initiation of anti-retroviral therapy during this period is associated with enhanced likelihood of recovery CD4positive counts (Le T et al).

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