Antigen-specific cytometry—New tools arrived!

Until recently, immunofluorescence-based cytometry and cell sorting, which have now found their place in the repertoire of state-of-the-art technologies, have mostly served to identify and assess subsets of leukocytes and thereby to evaluate rather systemic changes of the immune system. A more detailed defined evaluation of immune responses was not possible for a long time. In particular, a focus of the cytometric analysis on those lymphocytes specifically recognizing a defined antigen was hampered due to technical limitations. Yet, traditional methods for the analysis of antigen-specific lymphocytes typically relied upon measurements of proliferation or cytokine expression in bulk cultures. In recent times, this hindrance has been overcome both for B and T lymphocytes. We review here the emerging field of antigen-specific cytometry and describe the most widely used state of the art and future technologies that offer exciting new options to analyze and isolate specifically those lymphocytes that are directly involved in the immune reaction to given antigens, options that have already spurred research, diagnosis, and therapy beyond scope.