Springer Current Topics in Microbiology and Immunology: Volume 80

A variety of genetic and protein structural evidence suggests that two discrete genes - both a variable region gene and a constant region gene - specify each heavy chain and each light chain. This constitutes the two gene-one polypeptide hypothesis. Second, a single differentiated lymphocyte or plasma cell appears to express only one heavy chain allele and one light chain allele at a time. This is the only example of allelic exclusion known in mammalian cells except for X chromosome inactivation. Third, during the course of lymphocyte differentiation, there may be a switch of the heavy chain constant region gene expression but no change in the heavy chain variable region gene expression.