Lymphocyte subset depletion studies

Cells other than T lymphocytes also appear to be involved in tolerance induction. Depletion of macrophages inhibited tolerance induction and transfer studies with non-T cell fractions from tolerant animals was shown to confer tolerance to naive animals [29] Thus, tolerance induction by low doses of D-penicillamine appears to have a complex mechanism that includes various T cell subsets as well as non-T cells, that may be antigen presenting cells. 

These experiments demonstrated that IL-2 was inseparable from the lympho-kine capable of restoring antibody responses of B cells in populations of lymphocytes depleted of T helper cells. Although the exact target cell of the IL-2 in these studies was not determined, it seems likely that IL-2 was either enhancing antibody synthesis indirectly by the activation of a particular subset of helper T lymphocytes or directly by activation of the antibody forming B cell precursors. Even though the prevailing notion is that the IL-2 enhances antibody synthesis indirectly, recent experiments indicate that activated B lymphocytes may express receptors for IL-2. Therefore, the mechanism by which IL-2 enhances antibody production remains essentially unknown. 

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