Antitheta immunization affects hemopoietic colony growth in a theta-incompatible mouse system

Seeking a system with which to study the antitheta-sensitive regulatory cell (TSRC), other than the W/Wv anemic mouse, we tested a model which utilizes mouse strains differing almost exclusively in theta allotype. AKR/FuRd Thy 1.1 mice were immunized against CBA Thy 1.2 mouse thymocytes to produce antibody. The immunized mice were lethally irradiated and grafted with marrow cells from AKR/Cum Thy 1.2 mice. It was reasoned that in this situation antitheta-sensitive cells present in or produced by the graft will be destroyed, while theta-incompatible host cells may not be as capable of collaboration with the graft stem cells as are the graft's theta-compatible cells. Anti-Thy 1.2 immunization did not influence the number of spleen colonies formed by marrow from Thy 1.2 mice; but the colonies formed, especially the erythropoietic colonies, were reduced in size. Also, both the relative and absolute frequencies of erythropoietic colonies were decreased, while those of granulopoietic colonies were increased. Therefore, the destruction of antitheta-sensitive cells in this system resulted in decreased effectiveness of spleen colony growth and altered the differentiation pattern of colony-forming cells. These effects were not observed in control groups immunized with CBA tissues not bearing the Thy 1.2 antigen. This study further stresses the importance of the theta antigen in hemopoietic differentiation and may provide an alternative in vivo model for studying the TSRC.