CHARACTERIZATION OF SPLEEN CELLS CAPABLE OF INDUCING UNRESPONSIVENESS IN ALS-TREATED MICE

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Abstract
C3H/He skin allografts are significantly prolonged in ALS-treated B6AF1 mice by the injection of 50X106 C3H/He spleen cells 1 week postgrafting. To identify and characterize the spleen cell active in promoting graft survival, C3H/He spleen cells were separated on a discontinuous Percoll gradient and the various fractions were assayed for the ability to prolong skin graft survival in ALS-treated B6AF1 mice. In addition, unfractionated spleen and spleen fractions were depleted of specific cell populations before injection to determine the effect of various cell populations on graft prolongation. The active cell was recovered primarily in the 52.5% Percoll fraction. Cells in the 60% fraction also had a graft-prolonging effect, but not as significant as that of the 52.5% fraction. Depletion of Thy 1, Ia and Ig-positive cells from unfractionated spleen or spleen fractions did not decrease the graft-prolonging effect. Both FcγR-positive and FcγR-negative cells prolonged graft survival, but the FcγR- cells were the most effective. In contrast to the effect of spleen cells, lymph node cells and thymocytes are relatively ineffective in prolonging graft survival in ALS-treated mice. When lymph node lymphocytes and thymocytes were separated on a Percoll gradient, the cell population active in prolonging graft survival was recovered primarily in the 52.5% fraction. Treatment of the 52.5% fraction of lymph node lymphocytes or thymocytes with monoclonal antibody to Thy 1 before injection abrogated the graft-prolonging effect. These results indicate that the spleen cell(s) active in prolonging graft survival in ALS-treated mice is a non-T, non-B cell, as it lacks Thy 1, la, and Ig surface markers. Both FcγR+ and FcγR− spleen cells are effective in prolonging grafts, but FcγR− cells are the most effective. In contrast, the active cell in lymph node and thymus is Thy 1-positive, indicating that it is a T lymphocyte.

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