T-cell-activating monoclonal antibodies, reacting with both leukocytes anderythrocytes, recognize the guinea pig Thy-1 differentiation antigen: Characterization and cloning of guinea pig CD90

A glycophosphatidylinositol (GPI)-linked differentiation antigen expressed on guinea pig T and B lymphocytes was identified by several monoclonal anti bodies; it has been shown previously that this membrane protein induced str ong polyclonal T cell proliferation upon antibody binding and costimulation by PMA. Purification by immunoadsorption and microsequencing revealed that this T-cell-activating protein is the homologue of Thy-1 or CD90, In contr ast to the Thy-1 antigen of most other species, guinea pig Thy-1 has a much higher molecular weight, which is due to a more extensive N-linked glycosy lation, bringing the molecular weight of the total antigen up to 36 kDa. Mo lecular cloning of guinea pig Thy-1 indicated that the deduced molecular we ight of the protein backbone is 12,777 after removal of an N-terminal 19-am ino-acid leader peptide and cleavage of the 31 amino acids for GPI anchorin g the C-terminal end. Sequence comparison showed that guinea pig Thy-1 has an 82% homology to human and a 72% homology to mouse Thy-1 on the amino aci d level. Immunohistological staining of cryostat sections revealed intensiv e staining with the monoclonal antibody H154 on fibroblasts, fibrocytes, Ku pffer cells, alveolar macrophages, and mesangial cells. As observed in the human, mouse, and rat, Thy-1 is abundant in the guinea pig brain. Unlike Th y-1 expression in other species, guinea pig Thy-1 is strongly expressed on most resting, nonactivated B cells and, to a lesser extent, on erythrocytes , While treatment of erythrocytes and lymphocytes with GPI-specific phospho lipase C largely decreased reactivity with mAb H154, T cells retained the p roliferative response to antibody and phorbol esters. (C) 1999 Academic Pre ss.