Key adhesion molecules are present on long podia extended by hematopoietic cells

Background: We recently reported that Cd34⁺ hematopoietic cells and the KG1a cell line extend long, thin podia. These podia can dynamically extend and retract, often adhere to the substrate, and appear to connect cells up to 300 μm apart. The surface receptors found on these podia have not been described. Methods: By using time-lapse fluorescent microscoscopy and immunostaining techniques, we describe a method for detecting surface receptors on these podia. This includes an in situ antibody staining procedure without fixing cells. Results: We demonstrate, using CD34 selected mobilized peripheral blood cells and KG1a cells, that adhesion molecules known to play important roles in blood-cell migration and adhesion are present on these podia. These include: CD11a, CD18, CD29, CD34, CD45, CD49d, CD49e, and CD62L. Additionally, CD54 and CD44 were present on the podia extended by KG1a cells, but were not detectable on the primary Cd34⁺ cells. The integrin CD49d localized at the base of these podia in a time-dependent manner in KG1a cells. The frequency and morphology of these long podia on three myeloid leukemia-cell lines (KG1a, MV4-11, and AML-193) and a CD34- negative T-cell line (CEM) are also compared. KG1a and CEM cell lines extend long, dynamic podia that are similar to the podia on primary Cd34⁺ cells in morphology and adhesion molecule expression. The AML-193 and MV4-11 cell lines, however, did not extend these long podia. Conclusions: We describe a technique that provides a method of detecting surface receptors on thin cell membrane projections. These results support the likely role of these podia in cell migration and cell-cell communication.