A sensitive assay for the quantification of integrin-mediated adhesiveness of human stem cells and leukocyte subpopulations in whole blood.

Adhesion of leukocytes is an early step in the formation of adaptive or innate immunity. In chronic inflammatory pathologies like atherosclerosis, regulation of adhesiveness is pivotal for the accumulation of leukocytes within the vessel wall. Therefore, the quantification of adhesion is crucial for the understanding and monitoring of immune responses in patients. However, so far, functional analysis of leukocyte adhesion has been time consuming and required prior purification of cell populations from peripheral blood. This reduced the number of samples and cell populations that could be analysed from limited patient material. Here, we introduce a novel method involving rapid quantification of integrin-mediated leukocyte adhesion in human whole blood using flow cytometry. The quantification relies on soluble multivalent immunocomplexes and is thus called "ligand-complex-based adhesion assay" (LC-AA). LC-AA evaluates both integrin affinity and avidity in T-cells, NK-cells and monocytes from as little as 20 mul of whole blood. In marked contrast to T-cells and NK-cells, unstimulated monocytes show non-blockable background binding of the complexes. Therefore, for this subset only, the stimulation-induced integrin activation is measurable. With the LC-AA, for the first time, measurement of adhesiveness of extremely rare cell populations like CD34+ peripheral blood stem cells can be assessed in the absence of prior purification steps. Finally, the small blood volumes needed for adhesion analysis with the LC-AA allow the evaluation of multiple cell subpopulations in large sample collectives, e.g. required in clinical studies.