Response of mice to rabbit Fab' 2 and Fab'. Thymus independence of IgM response and thymus dependence of IgG response

Abstract

We have investigated the cell populations required for the in vivo and in vitro immune response of mouse spleen cells to rabbit Fab′₂ and Fab′ and sheep red blood cells (SRBC). The production of IgM antibodies to SRBC both in vivo and in vitro is dependent upon the presence of thymus-derived lymphocytes, although some response does occur in their absence. The IgG response can only be obtained in vivo, and is also dependent upon the presence of thymus-derived lymphocytes. By contrast, the in vivo and in vitro IgM response of mice to rabbit Fab′₂ and Fab′ is independent of the presence of thymus-derived lymphocytes, but the in vivo IgG response is thymus dependent. The in vitro response to both SRBC and rabbit Fab′₂ is low in cultures depleted of macrophages, but the rabbit Fab′₂ response appears less affected by macrophage depletion than the SRBC response.