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Review

Nature Reviews Immunology 2, 872–880 (1 November 2002) | doi:10.1038/nri935

Two-photon tissue imaging: seeing the immune system in a fresh light

Michael D. Cahalan , Ian Parker , Sindy H. Wei & Mark J. Miller

Many lymphocyte functions, such as antigen recognition, take place deep in densely populated lymphoid organs. Because direct in vivo observation was not possible, the dynamics of immune-cell interactions have been inferred or extrapolated from in vitro studies. Two-photon fluorescence excitation uses extremely brief (in vivo setting and to reveal in detail the cellular collaborations that underlie the immune response.