Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) activated PI3K-delta syndrome ?
    ### Response:
    Activated PI3K-delta syndrome is a disorder that impairs the immune system. Individuals with this condition often have low numbers of white blood cells (lymphopenia), particularly B cells and T cells. Normally, these cells recognize and attack foreign invaders, such as viruses and bacteria, to prevent infection.
    