Biochemical and functional analysis of mice deficient in expression of theCD45-associated phosphoprotein LPAP

The role of the CD45-associated phosphoprotein (LPAP/CD45-AP) during an imm une response remains unclear. To understand better the function of LPAP we generated LPAP-deficient mice by disrupting exon 2 of the LPAP gene. LPAP-n ull mice were healthy and did not show gross abnormalities compared to thei r wild-type littermates. However, immunofluorescence analysis of T and B ly mphocytes revealed a reduced expression of CD45, which did not affect a par ticular subpopulation. In contrast to a recent report (Matsuda et al., J. E xp. Med. 1998. 187: 1863-1870) we neither observed significant alterations of the assembly of the CD45/lck-complex nor of polyclonal T-cell responses. However, lymph nodes from LPAP-null mice showed increased cellularity, whi ch could indicate that expression of LPAP might be required to prevent expa nsion of lymphocytes in particular lymphatic organs rather than potentiatin g immune responses.