Interferon-γ (IFN-γ) is the only type II interferon. This proinflammatory cytokine is secreted by activated T cells and NK cells. It activates macrophages and endothelial cells and regulates immune responses by affecting APCs, T cells, and B cells. Production of IFN-γ by helper T cells and cytotoxic T cells is a hallmark of the Th1-type phenotype. Thus, high-level production of IFN-γ is typically associated with effective host defense against intracellular pathogens. The Human IFN-γ ELISpot assay is designed for the detection of human IFN-γ secreting cells at the single cell level and can be used to quantitate the frequency of human IFN-γ secreting cells. ELISpot assays are highly reproducible and sensitive, and can be used to measure responses with frequencies well below 1 in 100,000. ELISpot assays do not require prior in vitro expansion of T cells and they are suitable for high-throughput analysis using only small volumes of primary cells. As such, ELISpot assays are useful tools