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The Immune System

Understanding the Parts of Your Immune System

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Updated January 17, 2009

Your immune system is your body's natural defense against infection and illness. Specialized cells and organs all work in concert to protect your body and keep you healthy. Understanding these different parts of your immune system and how your immune system works will help you better understand HIV and AIDS.

Organs and Cells of the Immune System

  • Bone Marrow
    All the specialized cells of the immune system are formed in the bone marrow, where they mature. When they are fully mature they move into the blood stream where they do their work.

  • Thymus
    This small but important organ is where lymphocyte precursors become thymocytes, which in turn mature into T-cells. In addition, the thymus actually chooses which T-cells are best suited for the immune system. The remaining ones are eliminated by the body, assuring a healthy, effective immunity.

    What Are T-Cells?

  • Spleen
    You can think of the spleen as a filter for the blood. It catches foreign material in the blood and activates different types of immune system cells.

  • Lymph Nodes
    The lymph nodes filter foreign material from the lymph fluid. Fluid that drains from various tissues in the body collects in the lymph system and passes through the nodes, being filtered as it passes.

    Why Are My Lymph Nodes Swollen?

  • T-Cells: There are two subsets of T-cells: CD4 cells and CD8 cells. CD4 cells secrete factors that activate other white blood cells that participate in the immune response. HIV attacks CD4 cells, damaging the body's ability to initiate the immune response. CD8 cells are important in directly killing tumor cells, viral infected cells and some parasites.

    Understanding CD4 Cells and CD4 Counts

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