Antigen‐specific T cell suppressor factor (TsF): isolation of a cDNA clone encoding for a functional polypeptide chain of phosphorylcholine‐specific TsF

Abstract

A cDNA library of phosphorylcholine (PC)‐specific suppressor T hybridoma, 29‐C‐6, was constructed. By differential colony hybridization, 68 colonies were selected which hybridized with mRNA probes of two PC‐specific suppressor T hybridomas, 29‐C‐6 and 09‐M‐24–8, but not with those of BW5147. A hybridization translation assay revealed that only one combination of translation products of cDNA clones, p6–1 and p6–5, showed strong PC‐T cell suppressor factor (TsF) activity. Sequence analysis showed that p6–5 contained a specific cDNA sequence of about 800 base pairs (bp) while p6–1 had a 190 bp poly(A) sequence insert. When total poly(A)⁺RNA of 29‐C‐6 was hybridized with a p6–1 filter alone the recovered mRNA was capable of producing PC‐TsF. However, when the total poly‐(A)⁺RNA was hybridized with a p6–1 filter combined with a p6–5 filter, the mRNA eluted from the p6–1 filter was not able to produce PC‐TsF, suggesting that the depletion of p6–5 specific mRNA from p6–1‐binding poly(A)⁺RNA led to a complete abolishment of the capability to produce PC‐TsF. Furthermore, p6–5 hybridizing mRNA could successfully restore the p6–1‐binding poly(A)⁺RNA depleted of p6–5‐specific mRNA, and translation products of both RNA mixtures showed strong PC‐TsF activity. These results suggest that PC‐TsF is not a single polypeptide chain, but is composed of at least two distinct polypeptide chains, and also that p6–5 contains a cDNA sequence encoding for one of the polypeptide chains composing the PC‐TsF molecule.