An ELISPOT method of in vitro diagnosis of tuberculosis includes enriching or separating liquid blood fraction from its cellular components including visualizing immunocompetent cells by detecting different dyes and using at least two different filter sets, each including one narrowband excitation filter and one narrowband blocking filter, wherein the narrowband excitation filter is transmissive for light provided for luminescent excitation of a respective dye and the narrowband blocking filter is transmissive for light emitted by a respective dye and measuring the number of immunocompetent cells that secrete at least interferon-γ and interleukin-2 as a reaction to an antigen by superimposing at least two two-dimensional images generated during visualization to avoid luminescence of different dyes interfering and strong luminescence being superimposed on weak luminescence.