- Polymorphism of HLA-DR beta chains in DR4, -7, and -9 haplotypes: implications for the mechanisms of allelic variation. Gregersen, P.K., Moriuchi, T., Karr, R.W., Obata, F., Moriuchi, J., Maccari, J., Goldberg, D., Winchester, R.J., Silver, J. Proc. Natl. Acad. Sci. U.S.A. (1986)