Generation of diversity in mammalian gut-associated lymphoid tissues: restricted V gene usage does not preclude complex V gene organization.

The sheep genome contains 60 to 90 V lambda genes distributed in least 6 different families, whereas 37 V lambda genes and 10 families exist in humans. Comparison with human V lamda sequences indicates that sheep V lambda genes display less overall sequence divergence, but are closer to the genes most frequently used in the human peripheral repertoire. In both species, 2 to 3 genes contribute half of the expressed sequences. Therefore, similar large combinatorial potential and restriction of the expressed repertoire can exist in two species whose strategy of diversification differs widely (ongoing rearrangement throughout life in human bone marrow vs postrearrangement diversification during early development in sheep ileal Peyer's patches).