Freshly isolated unstimulated CD4⁺ T cells isolated from adult blood bind low levels of HTSU-IgG.

Lymphocytes were isolated by Ficoll-Hypaque gradient centrifugation from leukopaks of peripheral blood from adult donors. A portion of the cells were then analyzed by flow cytometry using the immunoadhesins (HTSU-IgG, 100 ng/mL, or SUA-IgG, 400 ng/mL) and anti-CD4 and either anti-CD45RA or anti-CD45RO antibodies as described in “Materials and methods.” Analysis was performed by gating on the population positive for binding to the CD4⁺ population, and binding of the immunoadhesins and the anti-CD45 antibodies was determined. The MFI of the immunoadhesin on each double-labeled population was then determined. The remainder of the cells was then separated by counter-current elutriation, and similar flow cytometric analyses were performed.