Dendritic cells enriched from swine thymus co-express CD1, CD2 and major histocompatibility complex class II and actively stimulate alloreactive T lymphocytes

Initial characterization and partial purification of thymic dendritic cells (DC) from miniature swine were carried out with the ultimate goal of using these cells to induce transplantation tolerance in this preclinical animal model. Immunohistochemical analysis of swine thymic tissue sections has sh own DC to be large cells located in the medullary and the cortico-medullary regions as evidenced by the presence of surrounding Hassal bodies. These c ells exhibit membrane processes and express the CD1, granulocyte/macrophage (G/M), and major histocompatibility complex (MHC) class II surface antigen s, as well as the S100 cytosolic and nuclear markers found in humans to be specific for DC. Dendritic cells were purified from thymi following collage nase treatment, Percoll gradient centrifugation, and adhesion steps to plas tic. Cells similar in morphology and phenotype to those described in tissue sections were detected in the lighter density layers of the gradient and r epresented 0.02% of the starting cell number. Removal of plastic nonadheren t cells showed enrichment levels similar to those reported for murine and h uman DC. Two-colour flow cytometric analysis of purified pig DC identified these cells as MHC class IIhi, CD1(+), CD2(+), and G/M+. The dendritic natu re of these cells was confirmed by their potent ability to stimulate allore active T lymphocytes. Modification of porcine thymic DC by transfer of allo geneic MHC genes and reinjection into the DC donor should permit testing of the role of this DC subset in the induction of transplantation tolerance.