Mechanisms of suppression in the transfer of contact sensitivity. Analysis of an I-J+ molecule required for Ly2 suppressor cell activity.

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Abstract
The passive transfer of contact sensitivity (CS) by immune cells can be inhibited with an antigen-specific T suppressor factor [TsF]. This factor is composed of 2 subfactors: an antigen-specific subfactor made by a Ly1+ cell (PCl-F) and an antigen nonspecific subfactor made by a Ly2+ T cell (TNBSA-F). The suppressive activity of the complete factor can be eliminated by depleting the assay population of Ly2+ cells, even though it is the Ly1+ cell in the population that transfers the adoptive immunity. This suggests that the Ly2+ cell in the assay population is needed to transduce the suppressive signal to the Ly1+ effector cell of DTH [delayed type hypersensitivity]. A Ly2+ cell from immune mice could be induced to produce a cell free subfactor that overcame the requirement for this Ttrans cell in the suppression of CS by TsF. The induction required only PCl-F, TNP[trinitrophenyl]-coupled spleen cells, and resulted in the production of an antigen-nonspecific I-J+ subfactor by immune Ly2+ cells. The need for the Ly2+ transducer cell could also be overcome by addition of an I-J+ molecule secreted by Ly1 T cells hyperimmunized to SRBC [sheep red blood cell]. A suppressor complex made from mixing the I-J+ molecule with TNBSA-F could directly suppress the functional activity of immune T cells not only to transfer CS, but also to deliver help to B cells in an in vitro PFC [plaque forming cell] response. This suppressive complex is antigen-nonspecific and does not require Ly2+ cells in the assay population for suppressive activity. Evidently, effector factors of the suppressor circuit require 2 molecules; 1 that contains the functional suppressor material and 1 that serves as a "schlepper", a molecule needed to deliver the suppression to the appropriate target cell. The ability to construct a functional suppressor complex from 2 subfactors raised against different antigens, using different immunization procedures, which were isolated from factors exhibiting different functional activities suggests that certain cells of the immune system may play a universal role in transducing the suppressive signal.