Fractionation of cells on a discontinuous Ficoll gradient. Study of subpopulations of human T cells using anti-T-cell antibodies from patients with systemic lupus erythematosus.

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Abstract
Patients with active systemic lupus erythematosus (SLE) had a decrease in a subpopulation of cells (fraction D) when peripheral blood lymphocytes were separated on a discontinuous Ficoll gradient. Preincubation of SLE cells at 37 degrees C for 30 min led to a marked decrease in this fraction, composed primarily of thymus-derived (T) cells. Supernates of such preincubations were found to cause a reduction in fraction D cells from normal humans. The active factor in the supernate was found to be an IgG antibody. Similarly, serum from patients with active SLE produced a reduction in fraction D cells from normal donors. This activity was also found in the IgG fraction, and could be absorbed with a pure T-cell population. Depletion of macrophages and complement did not reduce the SLE anti-T-cell antibody-mediated loss of cells from fraction D; however, heat-aggregated human gamma globulin led to impairment of the reaction. These findings suggest that antibody-dependent direct lymphocyte-mediated cytotoxicity may play a role in T-cell lymphopenia of SLE. It was further noted that the SLE anti-T-cell antibodies, in contrast to rabbit antihuman thymocyte serum, recognized fraction D cells but not fraction E cells from normals. Since both fractions are largely T cells, it appeared that the SLE serum was directed against cell-membrane antigenic determinants present on fraction D T cells, which were absent or reduced in quantity on fraction E T cells. Thus, evidence was presented indicating the presence of at least two subpopulations of cells in man. This was supported by differential absorption of the anti-T-cell sera with fractions D and E.