This proposal requests funds for the purchase of shared instrumentation for an immunology group, consisting of nine faculty members, nine postdoctoral fellows, eighteen predoctoral trainees, and eleven research assistants. The instrumentation will be used for research on the cellular and molecular events involved in the differentiation and activation of T and B cells. The approaches will include the analysis of precursor cells, molecular mechanisms of receptor gene rearrangement, the structural basis of receptor specificity and its regulation, and the activation of lymphocytes.