Clusters of Differentiation Definition

Clusters of differentiation – a system of classifying lymphocytes according to the collections of antigens on the surface of their cell membranes, also called CD markers. Each CD has a specific role in cell signaling and communication, guiding cell function and response. CDs are critical to the normal function of the immune system. Some of the major CDs are

  • CD-1, which populates B-cell lymphocytes and macrophages and has a role in antigen presentation
  • CD-2, which populates T-cell lymphocytes and natural killer (NK) cells and activates T-cells
  • CD-3, which populates T-cell lymphocytes and facilitates antigen binding (the ability of T-cell lymphocytes to receive biochemical messages)
  • CD-4, which populates T-helper cells (T-cell lymphocytes that direct immune response to infection) and is a key marker for monitoring the progression of hiv/aids
  • CD-5, which populates B-cell lymphocytes that produce immunoglobulin M (IgM)
  • CD-7, which populates T-cell lymphocytes in acute lymphocytic leukemia (ALL) and is a marker for stem cell leukemias
  • CD-8, which populates T-suppressor cells (T-cell lymphocytes that end the immune response) and is a key marker for monitoring the progression of hiv/aids


CD-4 has become an important marker in tracking the progression of hiv/aids, as HIV-1 and HIV-2 bind with this antigen to gain access to the body. CD-4 receptors are abundant on certain T-cell lymphocytes called T-helper cells (also called T4 cells). In health, CD-4 coordinates numerous aspects of the immune response.

When pathogens such as HIV bond with CD-4 receptors, they block the ability of CD-4 to signal other immune cells. This communication failure disrupts the immune system’s ability to mount an effective immune response. HIV also uses the Thelper cells to replicate itself, further spreading infection. In combination, these events allow opportunistic infection that can overwhelm the body.


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