Thymic Hormones, Viral Infections and Psychoneuroimmunology
Reconstitution of the resultant profound deficit in humoral and cell-mediated immunity by thymus grafts in cell impermeable diffusion chambers or by injection of thymic extracts provided convincing evidence for the existence of thymic hormones. Stress and emotional distress may influence the immune system via the central nervous system and/or endocrine mediation. The relevance of any particular mechanism hinges on the nature of the virus in question and on the way the viral antigens or virions are encountered, i.e. the phase of the infection. The specific response to viral antigens is almost entirely T-cell dependent, thus susceptibility to viral infection is particularly associated with T cell dysfunction. T cells are also required for most anti-viral antibody responses, which may serve to restrict spread of infection by viral neutralization and limit the extent of viremia which in turn prevents viral dissemination and affords protection against re-infection.