[Immunological tolerance]

[Long-term therapy using horse anti-dog lymphocyte globulin without sensitization against horse protein]

Eight mongrel dogs received a standard daily i.v. infusion of 20 mg/kg b.w. deaggregated horse-anti-dog-lymphocyte-globulin (ALG) and additional prednisolone (1 mg/kg b.w. daily i.v.) over a maximum period of 82 days following pretreatment with deaggregated normal horse IgG. No sensitization against horse protein was observed during therapy of afterwards as proved by lack of humoral antibodies against horse antigens, maintained lymphopenia, good compatibility, longterm prolongation of xenogeneic skin graft survival (85.6+/-20.6 days, n=8' untreated controls 12.5+/-1.3 days, n=4) and longterm suppression of cytotoxic antibodies against donor lymphocytes. The level of preformed agglutinating antibodies against horse erythrocytes was significantly reduced, while preformed antibodies against other species remained normal. The immune response to a challenge injection of anti-lymphocyte-serum (ALS) 6-11 weeks after termination of treatment was significantly lower in the ALG treated animals as compared to the control group. These results suggest the involvement of a specific mechanism of unresponsiveness against ALG other than immunosuppression only. It is concluded, that by the described method sensitization against ALG can be prevented during longterm treatment.

Tolerance to heterologous erythrocytes

Injection of a water-soluble nonantigenic fraction obtained from lysed sheep red blood cells virtually abolishes the subsequent immune response to the red cells. The suppression is systemic and appears to be serum mediated.