Mechanisms of immunosuppression.

Immunosuppresive disease is a major economic concern in domestic poultry production. Although many immunosuppressive agents have been described, mechanisms of how infectious and noninfectious agents compromise the immune system are poorly understood in avian species. Two categories, generalized and antigen-specific immunosuppression have been described in mammals. Generalized immunosuppression produces overall reduced responsiveness and increased susceptibility to a wide variety of infectious and neoplastic diseases. The best characterized immunosuppressive mechanisms are described in HIV-1 infections that lead to acquired immune deficiency syndrome (AIDS) in humans. In contrast, the antigen-specific suppression observed in human leprosy illustrates how an infecting agent selectively suppresses host responses against itself favoring bacterial spread. Both diseases have well-defined clinical staging classifications that correlate with specific immunological defects. An approach to studying immunosuppressive mechanisms in the avian suggests the need for relating pathogenesis with tests of immune responsiveness using a series of increasingly more specific immunological assays to pinpoint defects.