BriefDefinitive Report A NEW VARIABLE REGION IN MOUSE IMMUNOGLOBULIN A LIGHT CHAINS

The light chains of mouse Igs have been classified into two isotypes, K and X. In contrast to the x chains, the A chains were shown to display restricted heterogeneity . Two V.1 gene segments and four J.1-CA gene pairs have been described (1) . The three X subtypes (X1, X2, and a3) are respectively encoded by the combination of VA1J.11-C.11, VA2J.12-CA2, and V.11JA3-C.13 gene segments . The J.14-C.14 gene pair was never found to be functional (2, 3) . In the mouse, study of the X-bearing Igs is made difficult by the fact that they represent only 5% of total Igs (4) . Three strategies were described to increase their level in sera. The first method consisted in immunizing mice with antigens that are known to elicit X+ immune responses (5) . The second method consisted in producing rc-immunosuppressed mice by repeated injections of anticc antibodies (6) . We have previously described a third method, which is to inject mice with anti-X antibodies coupled to LPS (7, 8) . In this paper we describe BALB/c hybridomas obtained after injection with anti-X2 antibodies coupled to LPS and demonstrate the existence of an unexpected new X light chain .