Differential surface expression of MICA by endothelial cells, fibroblasts,keratinocytes, and monocytes

MICA is a new, highly divergent and poly morphic HLA-related gene that has a similar intron-exon organization as the HLA class I genes. Ir functions a s a restriction element for intestinal gamma delta T cells and it behaves a s a cell stress molecule. Ic is likely that the polymorphic MICA molecule m ay be target for specific antibodies and T cells in solid organ grafts or i n graft versus host disease (GVHD). Previously, we generated three MICA-spe cific sera in rabbits, which were used for Western blot, flow cytometry and immunoprecipitation. We demonstrated that MICA is expressed in endothelial cells, keratinocyes c and monocytes, bur not in CD4(+), CD8(+) or CD19(+) lymphocytes. We also found that MICA is expressed on the cell surface in He La cells. In the present work, per forming peptide neutralization assays, w e further confirmed the specificity of the reactivity of these sera against MICA. Also, by Western blot we demonstrate that freshly isolated human ski n-derived fibroblasts express MICA. We also investigated the surface expres sion of MICA in different, freshly-isolated cells. The results show that en dothelial cells and fibroblasts express MICA at the cell surface. Although expressing the 62 kDa MICA band, as detected by Western blots, keratinocyte s and monocytes do not seem to express this antigen on the cell membrane. T his differential surface expression of MICA by endothelial cells and fibrob lasts vs, keratinocytes and monocytes, may indicate that the levels of surf ace MICA are differentially regulated in different cells. Moreover, the exp ression of MICA on the surface of endothelial cells makes this polymorphic molecule a possible target during che immune response of graft rejection in organ transplantation. Human Immunology 60, 323-330 (1999) (C) American So ciety for Histocompatibility and Immunogenetics, 1999 Published by Elsevier Science Inc.