MOLECULAR-CLONING AND CHARACTERIZATION OF A CDNA-ENCODING MONOCLONAL NONSPECIFIC SUPPRESSOR FACTOR

The monoclonal nonspecific suppressor factor (MNSF) is a lymphokine pr oduct of a murine T-cell hybridoma that inhibits the generation of lip opolysaccharide-induced immunoglobulin-secreting cells in an antigen-n onspecific manner. A cDNA clone encoding MNSF beta (an isoform of MNSF ) was isolated and expressed in bacteria. The sequence obtained is vir tually identical to the Fau protein, a product of the ubiquitously exp ressed fau gene with unknown function. Northern blot analysis demonstr ated a single, 0.6-kb transcript. Specific polyclonal antibodies again st synthetic peptides corresponding to the deduced amino acid sequence s were elicited in rabbits. Immunoprecipitation experiments with these antibodies showed that MNSF beta is released extracellularly in an ag gregate form, albeit it lacks a signal peptide sequence. The anti-MNSF beta affinity eluate from the MNSF-producing murine hybridoma (E17) a nd concanavalin A-activated splenocyte culture supernatants inhibited the immunoglobulin production by lipopolysaccharide-activated splenocy tes. Recombinant MNSF beta also showed a similar biologic activity. Th us, ubiquitin-like protein(s) may be involved in the regulation of the immune responses.