Streptococcal group A carbohydrate has properties of both a thymus-independent (TI-2) and a thymus-dependent antigen

Streptococcal group A carbohydrate, which elicits mouse antibody of primarily the IgM and IgG3 isotypes, is relatively nonimmunogenic in nu/nu or xid mice, and thus appears to be a type of TD-2 antigen. The TD-2 antigens described previously have been proteins that elicit IgG antibody primarily of the IgG1 and IgG2 isotypes. Our findings indicate that TD-2 properties may also be a characteristic of at least some carbohydrate antigens that can elicit IgG antibody predominantly of the IgG3 class.