HUMAN ANTI-GAL HEAVY-CHAIN GENES - PREFERENTIAL USE OF V(H)3 AND THE PRESENCE OF SOMATIC MUTATIONS

Anti-Gal is the most abundant natural Ab known in humans. It interacts specifically with the carbohydrate structure Gal alpha 1-3Gal beta 1- 4GlcNAc-R (termed the alpha-galactosyl epitope), constitutes approxima tely 1% of circulating Ig, and is found in all three isotypes in the s erum. Anti-Gal is produced in Old World monkeys, apes, acid humans, an d in no other mammalian species. The objective of this study was to de termine the V-H genes involved in the synthesis of anti-Gal. B lymphoc ytes from various individuals were transformed by EBV, the clones prod ucing anti-Gal were isolated, the specificity and affinity of the Abs were determined, and the V-H genes were sequenced. The affinity of ant i-Gal clones for the free radiolabeled alpha-galactosyl epitope ranged between 1.1 x 10(6) M(-1) and 5 x 10(8) M(-1). Eight of the nine clon es studied used V(H)3 family genes and one clone used a V(H)1 family g ene. Four of the five V(H)3 genes used were found to form a cluster of related sequences, suggesting that functional constraints may lead to the use of V(H)3 genes with structural motifs that are suited for spe cific interactions with the alpha-galactosyl epitope. Comparison with known germline sequences for all of the clones studied and analysis of autologous germ-line genes in two of the clones indicate that anti-Ga l V-H genes undergo somatic mutations. These somatic mutations may pro vide a pool of variants that are available for affinity maturation.