[Pathogenetic mechanisms responsible for producing a secondary immunodeficiency state]

Abnormalities of the immune response can be secondary to old age, to several pathologic conditions (i.e. diabetes mellitus, renal failure, solid and lymphohematologic neoplasias, leukopenia, malnutrition, autoimmune diseases, AIDS), to surgical stress or to burns, and to immunosuppressive therapies, both medical (corticosteroids, cytotoxic agents, antilymphocytic globulins) and surgical (splenectomy) as well as radiant (extensive radiotherapy). Old age can affect both humoral (reduced antibody synthesis) and cell-mediated (thymus involution, diminished ratio Th/Ts, depression of both delayed hypersensitivity reactions and cytotoxic activity of K cells) immune response. Hyponutrition, often observed in the elderly, adds a reduced production of secretory IgA, lysozyme and interferon, diminished complementary activity, phagocytosis defects, and vitamin deficits. Furthermore, in some chronic diseases we can observe reduced primary antibody response or depression of delayed hypersensitivity reactions (renal failure, neoplasias), changes in leukocyte functions (diabetes mellitus, leukemias and lymphomas) and, in particular in solid neoplasias, increased activity of Ts lymphocytes and the presence of circulating immunocomplexes. Changes in phagocytosis, opsonization and chemotaxis are typically seen in burns, whereas surgical stress can cause some inhibition of cell-mediated immunity. Finally, after splenectomy it is possible to observe an increased synthesis of IgA and IgG and, on the contrary, reduced production of IgM and properdin.