We cloned the cDNAs encoding the feline homologues of B-lymphocyte activation antigens B7-1 (CD80) and B7-2 (CD86). We expressed recombinant feline CD80 and CD86 molecules by the baculovirus expression system, and demonstrated their binding ability to human CTLA4-murine immunoglobulin fusion protein. The B-cell activation antigens B7-1 (CD80) and B7-2 (CD86) are homologous molecules expressed on the antigen presenting cells, interact with the T-cell antigen CD28 and the cytotoxic T-lymphocyte-associated protein 4 (CTLA4), and play important roles in regulation of the immune system (Lenschow et al., 1996). Recently, we cloned the cDNAs encoding the feline CD28 (fCD28) (Nishimura et al., 1999) and CTLA4 (fCTLA4) (Nishimura et al., 2000) homologues which conserved the hexapeptide motif (MYPPPY) known as the important region for binding of CD28 to CD80 in humans (Peach et al., 1994). However, there was no information about feline CD80 (fCD80) and CD86 (fCD86) molecules, and their function and role in feline immune system have not been discussed yet. In this study, we cloned and sequenced the cDNAs encoding the fCD80 and fCD86 homologues which interact with human CTLA4-murine immunoglobulin (Ig) fusion protein.
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