The characterization of the toad splenocytes which bind mouse anti-human IL-2 receptor antibody.

We have utilized two depletion protocols to characterize the spleen cells of the South African clawed toad, which bind specifically mouse-anti-human IL-2 receptor (anti-Tac) antibody and recombinant DNA produced IL-2. When the selectively lymphotoxic reagent, N-CH3-N-nitrosourea (NMU), is injected into adult toads, it removes the thymic cortex and lymphocytes throughout the body required for helper and cytotoxic cell functions. We have also used a monoclonal mouse anti-Xenopus IgM antibody to deplete toad splenocyte populations of surface (s) Ig+ cells. Freshly biopsied and cultured spleen cells were compared with respect to their capacity to bind fluorescent (Fl*-) anti-Tac antibody and its ligand, rIL-2, after a depletion protocol. The results clearly show that a phytohemagglutinin (PHA)/IL-2 sensitive splenocyte population is removed by NMU injection. While many of the remaining NMU insensitive, previously cultured cells are Tac+, they fail to bind rIL-2. Freshly biopsied spleen cells with constitutive IL-2 receptors are found in both the sIg- (T cell enriched) and sIg+ (B cell enriched) populations following panning. Moreover, both populations are able to bind the ligand with equal efficiency. Thus, constitutive IL-2 receptor bearing cells are not restricted to either the T or B cell populations. The predominant PHA activatable, rIL-2 binding cell populations of the toad appear to be T cells which are involved with helper and cytotoxic functions.