PRINCIPLES OF VACCINOLOGY: THE UTILIZATION OF THE IMMUNE SYSTEM TO MAKE A VACCINE EFFECTIVE

摘要

When evaluating vaccines used in veterinary medicine, serum antibody titer is often cited as an important measure of vaccine efficacy. Yet, in a number of diseases, serum antibody levels are not a good predictor of protective immunity. Specific antibodies to some infectious agents do not adequately protect the host from infection and disease. In addition, antibodies to certain infectious agents can enhance disease. One mechanism for this antibody-dependent enhancement is when immunoglobulin-bound pathogens rely on Fc receptor-mediated phagocytosis for entry to host cells. Immune complexes can also contribute to the pathogenesis of infectious diseases by triggering complement activation and inducing a type III hypersensitivity response. Another factor to consider is that antibodies may not always be detectable following an adaptive immune response. For several viral agents, adaptive cell-mediated immune responses can be mounted in the presence of passively transferred maternal antibody, even while humoral responses are suppressed. Thus, animals with no detectable antibody titers can be fully resistant to challenge.