title: Serum requirements for in vivo modulation of thymus-leukemia antigens on mouse leukemia cells and thymocytes.
abstract: Mouse leukemia cells and normal thymocytes bearing thymus-leukemia (TL) cell surface antigens were previously shown to acquire resistance to lysis by guinea pig complement (C) during incubation with TL alloantiserum in vitro at 37 degrees C due to heat-labile serum activity resulting in deposition of mouse C3 onto the cell surface. The role of heat-labile serum activity and C3 in modulation of TL+ cells in vivo in mice actively or passively immunized against TL antigens was investigated. Mice of the TL-/TL+ C57BL/6J (B6) strain and the B6 congenic strain B6-Tiaa possessed poorly modulating sera, and the radiation-induced A-strain leukemia RADA1 transplanted into B6 mice passively immunized with heated (56 degrees C) TL antiserum failed to modulate; thymocytes of B6-Tiaa mice immunized similarly also did not modulate. A specific requirement for mouse C3 deposition onto RADA1 cells to achieve a modulated state was demonstrated in actively immunized TL- (B6 X A-Tiab)F1 mice in which circulating C3 and modulating activity were depleted by administration of cobra venom factor. In immunized (B6 X A-Tiab)F1 mice bearing RADA1 transplants and repeatedly given injections of B6 serum, tumor cells escaped immune destruction despite a lack of modulation. Thus modulation of TL antigenicity on tumor cells in vivo, but not tumor escape, required cell-bound C3.
mesh_terms: D000818:Animals; D000912:Antibodies, Neoplasm; D000951:Antigens, Neoplasm; D003176:Complement C3; D003602:Cytotoxicity, Immunologic; D005260:Female; D007116:Immunization, Passive; D007165:Immunosuppression Therapy; D066298:In Vitro Techniques; D007942:Leukemia, Experimental / Q000276:immunology*; D008297:Male; D051379:Mice; D013601:T-Lymphocytes / Q000276:immunology*; D013953:Thymus Neoplasms / Q000276:immunology*
chemical_list: D000912:Antibodies, Neoplasm; D000951:Antigens, Neoplasm; D003176:Complement C3