The overall goal of this program project grant is to study the mucosal barrier to infectious agents. This Core provides a facility for Live Cell Multiphoton and Confocal Imaging. Mucosal surfaces are largely lined by a monolayer of epithelial cells. These cells are highly polarized, with separate apical and basolateral surfaces. These cells are typically 10-15 microns tall. It is therefore essential to study these cells using an imaging system which provides good three-dimensional information. Conventional microscopy does not provide an adequate appreciation of separate events happening at the apical or basolateral surfaces. Moreover, we our work involves imaging dynamic processes in live cells. This requires time lapse capability (4 dimensional imaging) and the minimization of phototoxicity. We have found that multiphoton confocal microscopy works best for our needs. This Aims of this Core are to: 1. Provide a core facility for a multiphoton confocal microscope, suitably equipped for time lapse imagining of epithelial cells and interaction of epithelial cells with inflammatory cells. 2. Provide technical support and instruction for proper maintenance and operation of this microscope and for analysis of the data. The Core contains a new Zeiss 510 Confocal Microscope built on an inverted Zeiss microscope, equipped with a Coherent pulsed laser system for multiphoton microscopy. The system is completely equipped with all of the accessories needed, including all needed objectives, chamber for control of temperature and gas, computers, and software licenses.