The majority of human tonsillar CD5⁺ B cells express somatically mutated V_χ4 genes

We have fractionated human tonsillar B cells on the basis of CD5 expression and determined the nucleotide sequences of immunoglobin light chain variable (V) regions encoded by the single member of the V_χ4 gene family in both CD5⁺ and CD5⁻ populations. The majority of cDNA from both CD5⁺ and CD5⁻ B cells populations harbored somatic mutations. Thus, human tonsillar CD5⁺ B cells, unlike their murine counterparts, are capable of activating their somatic hypermutation mechanism, resulting in the accumulation of somatic mutation in the V_L regions.