IMMUNOGLOBULIN HEAVY-CHAIN GENE-EXPRESSION IN PERIPHERAL-BLOOD B-LYMPHOCYTES

cDNA libraries for IgM heavy chain variable regions were prepared from unmanipulated peripheral blood lymphocytes of two healthy people. Partial sequencing of 103 clones revealed V(H) gene family use and complete CDR3 and J(H) sequences. The libraries differed in the two subjects. In one person's cDNA the V(H)5 family was overexpressed and the V(H)3 family underexpressed relative to genomic complexity. In the second person's cDNA, V(H)3 was most frequently expressed. In both libraries, J(H)4 was most frequent. V(H) segments of several clones were closely related to those in fetal repertoires. However, there was also evidence of mutation in many cDNAs. Three clones differed from the single nonpolymorphic V(H)6 germline gene by 7-13 bases. Clones with several differences from V(H)5 germline gene V(H)251 were identified. CDR3 segments were highly diverse. J(H) portions of several CDR3's differed from germline J(H) sequences. 44% of the clones had D(H) genes related to the D(LR) and D(XP) families, most with differences from germline sequences. In 11 D(LR2)-related sequences, several base substitutions could not be accounted for by polymorphism. Thus, circulating IgM-producing B cell populations include selected clones, some of which are encoded by variable region gene segments that have mutated from the germline form.