(1) Immunodeficiency diseases can be divided into two categories according to the etiology: primary immunodeficiency diseases and secondary immunodeficiency diseases. According to the different immune components involved, it can be divided into humoral immunodeficiency, cellular immunodeficiency, combined immunodeficiency, phagocytic dysfunction and complement deficiency.

(2) The common characteristics of immunodeficiency diseases are: increased susceptibility to infection by various pathogenic microorganisms; The incidence of malignant tumor is higher than that of normal people of the same age, especially those with T cell immunodeficiency. It is easy to be accompanied by autoimmune diseases.