Efforts to develop a new, more effective vaccine for tuberculosis have been hampered by a
lack of understanding of what constitutes a protective memory immune response. While
interferon γ production by CD4+ T cells after vaccination is commonly used as a surrogate of
protective memory immunity, its use in this regard appears to have little predictive value. We
argue that this is due to the different requirements for interferon γ-mediated protection in the
primary response versus the memory recall response. In this review, we present evidence …