Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) mannose-binding lectin deficiency ?
    ### Response:
    Mannose-binding lectin deficiency is a condition that affects the immune system. People with this condition have low levels of an immune system protein called mannose-binding lectin in their blood. These individuals are prone to recurrent infections, including infections of the upper respiratory tract and other body systems.
    