Structure and expression of ovine complement receptor type 2

The structure of sheep complement receptor type 2 (CR2) was characterised b y cDNA cloning, protein sequencing and immunoprecipitation. The primary str ucture of sheep CR2 is similar to known mammalian homologues but the higher -order structure is unusual. Two distinct CR2 isoforms occur, one of which is ubiquitinated in the cytoplasmic domain, and the two molecular forms are expressed at the cell surface as non-covalently associated dimers. The per centage of sheep B-cells that express CR2 changes during development and va ries between different body compartments. CR2(+) and CR2(-) B-cell subsets also differ in the expression of other surface markers and in functional pr operties. Differential expression of CR2 may, therefore, delineate B-cells that arose by alternative developmental pathways, or it could be a marker f or B-cells at different phases of antigen exposure. (C) 1999 Elsevier Scien ce B.V. All rights reserved.