An antisense phosphorothioate (S)-oligonucleotide to a sequence in the intervening (I) region of the gamma 2b immunoglobulin (Ig) heavy chain gene inhibits Ig secretion by B cells stimulated with lipopolysaccharide (LPS) or LPS plus interleukin 4. It is also a striking stimulant of DNA synthesis by resting B cells. The antisense S-oligonucleotide causes a 10-20-fold increase in the expression of the gamma 2b germline transcript. Among mutants of the antisense S-oligonucleotide, some show all the effects whereas others are inactive. A similar hierarchy exists in the quantitative biological activities of mutant S-oligonucleotides and in their capacity to hybridize to the sense oligonucleotide, strongly suggesting that an I gamma 2b sequence in the RNA transcript or in the noncoding strand of the DNA is the target of the antisense S-oligonucleotide. The possible relationship of the overexpression of the germline gamma 2b transcript to the biological functions of the I gamma 2b antisense S-oligonucleotide is discussed.

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