The experiments proposed in this grant rely heavily on close collaborative interactions amongst the three PIs. The Core component will greatly facilitate these interactions. Core B is divided into 3 components: a) breeding of transgenic/knockout mice, b) maintenance of conventional transgenic and knockout mice, and c) flow cytometry. Core B is designed to provide aged T cell receptor transgenic, gene knockout and conventional mice that are required by all three projects of the program. Core B will breed and screen transgenic animals (using FACS or PCR analysis) and backcross them as necessary to render them suitable for the experiments detailed in the individual projects of the program. Because this process is very labor intensive, a centralized facility specialized to perform this task is essential. The core will obtain the various aged conventional, transgenic or knockout mice needed for the individual projects, quarantine them if necessary, develop standardized procedures for screening for the transgenic/knockout gene expression in each case, and will breed and backcross the mice to inbred strains. The goals are to have healthy, genetically homogeneous mice for the investigators in the project. Investigators will be able to obtain these mice for experiments but will maintain the animals separately during the course of the sometimes lengthy adoptive transfer experiments. Each of the three projects relies heavily on the use of flow cytometry to assess the expression of various cell surface markers. The costs for FACS analysis is included in Core B because: 1) all three projects will rely heavily on the use of the common FACS facility; 2) screening of the aforementioned animals require the use of flow cytometry and 3) many of the studies involving flow cytometry represent collaborative interactions among the PIs.