CD4+ cells are a specific type of white blood cell, also known as T lymphocytes, that play a central role in the body’s immune system. Often called “helper T cells,” they coordinate immune responses. They are characterized by the presence of a protein called CD4 on their surface. These cells are a subset of T cells that mature in the thymus, originating from stem cells in the bone marrow.
Role in the Immune System
CD4+ cells direct other immune cells to combat various threats. They identify pathogens such as viruses, bacteria, and fungi by recognizing specific antigens presented by other immune cells. This recognition triggers the release of chemical messengers called cytokines.
These cytokines activate immune responses throughout the body. For instance, CD4+ cells stimulate B cells to produce antibodies that target and neutralize foreign invaders. They also activate cytotoxic T cells, which kill infected host cells or cancerous cells. This coordination is central to the adaptive immune system, enabling the body to mount a specific and effective defense against diverse pathogens.
Measuring CD4+ Cell Counts
CD4+ cell counts are measured by a blood test using flow cytometry. A blood sample is collected, and CD4+ cells are stained with a fluorescent dye. The flow cytometer analyzes the cells’ properties, counting those affected by the dye.
Results are reported as CD4 cells per cubic millimeter of blood (cells/mm³). A normal range for healthy adults is 500 to 1,200 cells/mm³, though values can vary between laboratories. This test monitors immune health and helps diagnose conditions affecting the immune system.
What Changes in CD4+ Cell Counts Indicate
Changes in CD4+ cell counts can signal underlying health issues, with both low and high counts having implications. A low CD4+ cell count is significant in human immunodeficiency virus (HIV) infection. HIV targets and destroys CD4+ cells, weakening the immune system over time.
As CD4+ cells decline, individuals become more susceptible to opportunistic infections, which are illnesses caused by pathogens that typically do not affect people with healthy immune systems. A CD4 count below 200 cells/mm³ is a diagnostic criterion for acquired immunodeficiency syndrome (AIDS), the most advanced stage of HIV infection, indicating a severely compromised immune system and a high risk of life-threatening infections. Other factors can also lead to reduced CD4+ cell counts, including certain cancers like leukemia or lymphoma, chemotherapy, radiation therapy, some autoimmune diseases, and severe infections like the flu or pneumonia.
Conversely, elevated CD4+ cell counts are less common but can occur in some conditions. While not as frequently indicative of severe illness as low counts, higher-than-normal CD4+ levels can sometimes be observed in certain autoimmune disorders or specific types of leukemia. Monitoring these counts provides healthcare providers with valuable information about the immune system’s status and helps guide treatment decisions, particularly in managing chronic conditions that affect immune function.