Which are examples of causes of secondary immunodeficiency? Select all that apply.

Secondary immunodeficiency develops because of an illness or an outside factor that weakens the immune system. HIV damages immune cells, leukemia can disrupt immune-cell production, and splenectomy removes an organ important for fighting certain infections. Humoral immunity is a part of the immune system, and antigens trigger immune responses; neither is itself a cause of secondary immunodeficiency.

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