How does the immune system fail in immunodeficiency diseases?

The immune system may fail in one of two ways in immunodeficiency diseases. Either the immune system fails to develop normally, as in severe combined immunodeficiency disease (SCID), or the immune response is blocked in some way, as in acquired immunodeficiency syndrome (AIDS). Treatment with immunosuppressive agents, such as radiation or specific drugs, may also result in immunodeficiency diseases.

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