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Certain rabbits produce high concentrations of yG antibodies to streptococcal carbohydrates after primary intravenous immunization with streptococcal vaccines.'-3 The electrophoretic behavior of these antibodies and their isolated light chains points to a markedly restricted population of 'yG molecules. This type of response is not found in all immunized rabbits. It may depend on the structure of the carbohydrate antigen, the intravenous route of immunization, the genetic background of the rabbits, and prior sensitization with the same or a related antigen. The rabbits in the present study did not respond in this way after primary immunization, but they did produce a high level of relatively homogeneous antibodies after secondary immunization. This suggests that in some instances prior sensitization may lead to a restricted population of yG antibodies.Materials and Methods.-Streptococcal vaccines: The vaccines were prepared from groups A, A-variant, and C streptococci as previously described.'Streptococcal group-specific carbohydrates: Groups A, A-variant, and C carbohydrates were isolated from hot formamide digests of cell walls.4Immunization: New Zealand red rabbits were immunized intravenously 3 times a week for 3 weeks with groups A or A-variant streptococcal vaccines. ' From 3 to 6 months following the first immunization, second series injections were given 3 times a week for 2 weeks. Sera were collected prior to each immunization period and at weekly intervals throughout immunization. Each sample of blood was collected 4 days after the last intravenous injection of vaccine.Serological, immunochemical, and electrophoretic methods: These were previously described.' Disc electrophoresis was performed at pH 8.3 in acrylamide gels by the method of Davis.-Total serum protein was determined by the Biuret method;6 concentrations of albumin and globulins were calculated from the densitometric scan of the zone electrophoresis pattern and the total protein value.

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