Infectious mononucleosis: a polyclonal B cell transformation in vivo.

We obtained spontaneous formation of Epstein-Barr virus-transformed B lymphocyte colonies from the blood of four patients with mononucleosis with the use of soft-agar medium. The colonies were propagated into separate cell lines and analyzed for their immunoglobulin secretion. Of 52 such lines, 44 produced immunoglobulin composed of a single class of heavy chain and single type of light chain. Among these clonal transformants, 27 (62%) of 44 produced mu-chain, 13 (29%) of 44 produced gamma-chain, and 4 (9%) of 44 produced alpha-chain. Analysis of light-chain secretion revealed that of the 44 cell clones secreting complete, monoclonal immunoglobulin products, 31 produced kappa-chain and 13 produced gamma-chain. One clone secreted mu-heavy chain and no light chain, an observation suggesting the clone is a pre-B cell phenotype. Seven lines derived from clones had aberrant patterns of immunoglobulin secretion that produced either two heavy chains or two light chains. B lymphocytes in different states of immunoglobulin gene expression are, therefore, transformed in vivo by Epstein-Barr virus.