One of the causes of variations in the expressed human T cell receptor (TCR) BV (V beta) repertoire is genetic variation in the germline DNA. Herein evidence is provided that allelic polymorphism may affect recombination frequency for a specific V gene. Two alleles of the TCR BV3 differ only at a single nucleotide position (C/T) within the 23-bp spacer region of the recombination signal sequence. These alleles are associated with variable percentages of BV3 cells in the peripheral blood, as shown in families and in unrelated normal donors. Individuals homozygous for allele 2 have a mean of 8.1% BV3 cells, heterozygous individuals have a mean of 4.7% BV3 cells, and homozygotes for allele 1 have a mean of 1.2% BV3 cells in CD3+ CD4+ peripheral blood T cells. Since the correlation is tight in unrelated individuals and other genetic differences were not found in the vicinity of BV3, we suggest that the spacer region sequence itself modifies recombination efficiency. This allelic system provides an example of a novel mechanism by which cis-acting genetic elements may affect recombination in a natural in vivo system.

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