Thymic nurse cells (TNC) are multicellular complexes composed of morphologically intact thymocytes internalized within epithelial cells. Due to their unusual features, they have been suspected to provide an appropriate microenvironment for T-cell repertoire acquisition. In recent functional studies in the chicken system, we have shown that intra-thymic nurse cell-lymphocytes (TNC-L) are highly efficient inducers of a graft-versus-host reaction (GvHR) in an allogeneic chorionallantoic membrane (CAM) assay, manifested by the formation of visible colonies, so-called pocks. Immunohistochemical and electron microscopical assessment of pocks revealed no differences between the cellular components and ultrastructural features of GvHR induced by TNC-L or peripheral blood lymphocytes (PBL). In addition, the stimulation of this local GvHR by interleukin 2 (IL-2) was demonstrated.