Monoclonal anti-IgM can separate T cell from B cell proliferative responses in the frog, Xenopus laevis.

The role of SIgM+ lymphocytes in frog mitogen responses and mixed lymphocyte reactions was examined. A murine monoclonal antibody with specificity for Xenopus laevis IgM was produced. The anti-IgM activity was not inhibited by glycoproteins other than Xenopus IgM, but could be inhibited with periodate-treated frog IgM. Fluorescent microsphere-coupled anti-IgM was used to show that adult and larval thymocytes had few sIgM+ lymphocytes, whereas spleens contained 19 to 34% sIgM+ lymphocytes. The spleens of larvally thymectomized adults were greatly enriched for sIgM+ cells. Lymphocyte suspensions were depleted of sIgM+ cells by incubation of spleen cells on plastic Petri dishes coated with anti-IgM monoclonal antibody. Compared with unseparated controls, the nonadherent cells cultured in serum-free medium were enriched for Con A and PHA mitogen responses and mixed lymphocyte culture (MLC) reactivity. Nonadherent cells were partially depleted of LPS mitogen responsiveness. Depletion or enrichment of the mitogen response was not a result of changes in kinetics or dose-response characteristics of the cells. In 1% FCS-supplemented cultures, the LPS response was not depleted, whereas the PHA response was still enriched. Thus, thymus-dependent and thymus-independent mitogen and MLC responses can be separated by the criterion of sIgM positivity in this anuran species.