Stimulation of human bone marrow stromal cell tyrosine kinases and IL-6 production by contact with B lymphocytes
Jarvis, L.J.; LeBien, T.W.
Journal of Immunology 155(5): 2359-2368
1995
ISSN/ISBN: 0022-1767 PMID: 7544372 Document Number: 442748
The interaction of normal human B cell precursors with the bone marrow (BM) stromal cells that support their growth and maturation is mediated by adhesion of B cell CD49d/CD29 (alpha-4-beta-1 integrin or VLA-4) to stromal cell CD106 (vascular cell adhesion molecule-1). To investigate whether this interaction is involved in stromal cell signal transduction, we generated CD49d-deficient variants of the RAMOS early B Burkitt's lymphoma cell line. RAMOS was chosen due to its lack of expression of CD49e (alpha-5 integrin) and CD44, which could potentially interact with stromal cells or their extracellular matrix. In contrast to the parental RAMOS cell line, CD49d-deficient RAMOS cell lines did not adhere to primary human BM stromal cells. Tyrosine phosphorylation of several stromal cell proteins was stimulated within 5 to 10 min of contact with either CD49d-expressing or CD49d-deficient RAMOS. These proteins included a 110-kDa substrate tentatively identified as pp125-FAK. In contrast, mAb cross-linking of stromal cell CD106 had no significant effect on protein tyrosine phosphorylation. IL-6 production by stromal cells was enhanced up to fourfold over 3 days when stromal cells were cultured in contact with RAMOS cells, regardless of CD49d expression. Stromal cell IL-6 production was not significantly enhanced by RAMOS cells cultured above the stromal cells in Transwell inserts. Thus, we have demonstrated through the use of paired CD49d-expressing and CD49d-deficient RAMOS cell lines that protein tyrosine kinase activity and IL-6 production by primary human BM stromal cells can be enhanced in a manner that is dependent on B cell contact but independent of CD49d-mediated adhesion. These results indicate the potential for B cells to interact with cells in their microenvironment and activate feedback mechanisms mediated by stromal cells, which may regulate lymphopoiesis.