IN UTERO SUPPRESSION OF K2 ISOTYPE IN HOMOZYGOUS BAS/BAS RABBITS THROUGH EMBRYO TRANSFER

Allotypes of rabbit Ig provide a useful tool for the study of quantitative expression of alternative allelic forms. In the rabbit, maternal Ig is transmitted to the foetus and protects the immunologically immature newborn during several of the first weeks of life. Induced maternal antibodies directed towards a paternally inherited allotype of the offspring can influence the expression of that allotype drastically. Normal Ig level in heterozygous allotype suppressed animals is provided by increased expression of the alternative allele. On the other hand, allotype suppression in homozygous animals leads to increased expression of non-allelic alternative gene products. We quantitatively analysed the expression of bas, a marker on the kappa 2 light chain isotype of the mutant strain Basilea, in homozygous bas/bas rabbits which had been fostered in utero of b4/b6 mothers producing anti-bas. All of the offspring studied expressed the kappa 2 isotype at a very low level at two months of age, and, in some individuals, bas was hardly expressed after 6 to 12 months. A suppressed rabbit, which was immunized to produce auto-antibodies against bas, continued to do so for at least 2.5 years. The long duration of homozygous bas suppression contrasts with homozygous suppression of other allotypes (CL kappa 1 and VHa) which generally lasts for a much shorter period.