Shared circulation in parabiosis leads to the transfer of bone phenotype from gld to the wild-type mice.

We have previously shown that mice with generalised lymphoproliferative disorder (gld) have increased bone mass in addition to autoimmune disease characterised by the accumulation of double negative (dn) T lymphocytes (CD3(+)CD4(-)CD8(-)CD45R(+)). To further explore the association of the immune disorder with the bone phenotype of gld mice, we established parabiotic circulation between gld and wild-type animals (C57BL/6, B6). One week after the surgery, the proportion of dn T lymphocytes increased in peripheral blood, bone marrow, spleen, and lymph nodes of wild-type members of the B6-gld parabiotic pair and decreased in tissues of gld pair members. The mixing of cells continued during four weeks of parabiosis. Number of osteoclast-like (OCL) cells in bone marrow cultures from a wild-type member of B6-gld parabiotic pair at the end of the first week decreased from 266+/-52 to 120+/-5OCL/cm(2), P<0.05, comparable with gld mice (99+/-21OCL/cm(2)), while the number of osteoblast colonies did not change. After four weeks, number of OCL cells formed from the bone marrow of B6 parabiotic mice was still similar to the number of OCL cells in their gld counterparts (150+/-18 and 131+/-24OCL/cm(2), respectively). In addition, the number of osteoblast colonies in B6 members of B6-gld parabiotic pairs increased (from 6+/-2 to 18+/-1colonies/cm(2), P<0.05) thus resembling the cell cultures of gld mice (18+/-1colonies/cm(2)). Taken together, these data show that the circulation of cells, including dn T lymphocytes established by parabiosis confers the osteoclast and osteoblast phenotype of gld to wild-type animals.