ANTI-B CELL AUTOANTIBODIES ENCODED BY V-H-4-21 GENES IN HUMAN FETAL SPLEEN DO NOT REQUIRE IN-VIVO SOMATIC SELECTION

We isolated immunoglobulin (Ig) V(H)4 genes that were rearranged in th e genomic DNA of 160 day human fetal spleen. Productively rearranged V -H 4-21 genes were cloned into pRTM1, a human IgM expression vector. T his allowed us to generate IgM(kappa)-expressing transfectomas by co-t ransfecting each of these constructs with pSVG-(kappa)3, an Ig kappa. Light-chain expression vector that has a variable region encoded Humkv 325, a conserved V-kappa gene that is frequently expressed early B cel l ontogeny. We find that all transfectomas expressing IgM(kappa) encod ed by V-H 4-21 make IgM auto antibodies reactive with i, a linear poly -N-acetyllactosamine determinant present on neonatal red blood cells a nd a B cell-restricted isoform of the CD45 surface molecule. In contra st, a transfectoma expressing pSVG-T-kappa 3 and pRTM1 containing a re arranged V(H)4-59 (V71-4) gene isolated from a chronic lymphocytic leu kemia B cell population, designated WIL, produced IgM(kappa) antibodie s that had no detectable anti-i binding activity. However, transfectom as expressing V-H 4-21 fused onto the Ig heavy-chain third complementa rity determining region (CDR3) of WIL are found to make anti-B cell au toantibodies with anti-i activity. These studies indicate that V-H 4-2 1 genes rearranged in human fetal B cell ontogeny can encode anti-B ce ll autoantibodies with a binding specificity that does not require in vivo somatic selection.