Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Antiphospholipid Syndrome ?
    ### Response:
    Antiphospholipid syndrome (APS) is an autoimmune disorder caused when antibodies -- immune system cells that fight off bacteria and viruses -- mistakenly attack healthy body tissues and organs. In APS, specific antibodies activate the inner lining of blood vessels, which leads to the formation of blood clots in arteries or veins.
    