IFN-γ (Interferon-gamma) is produced mainly by activated T cells and NK cells. Production of IFN-γ (Interferon-gamma) by helper T cells as well as cytotoxic T cells is a hallmark of the TH1-type phenotype, thus, high-level production of IFN-γ (Interferon-gamma) is typically associated with effective host defense against intracellular pathogens. The Enzyme-Linked ImmunoSpot (ELISpot) assay is commonly used to assess the function of antigen specific T cells by detecting IFN-γ release. The ELISpot assay is a very sensitive immunoassay, allowing the detection of a secreted cytokine at the single cell level. With detection levels that can be as low as one cell in 100,000, the ELISpot is one of the most sensitive cellular assays available. Depending on the substance analyzed, the ELISpot assay is between 20 and 200 times more sensitive than a conventional ELISA.