(Reuters) -Johnson & Johnson ( JNJ ) is in discussions to buy Protagonist Therapeutics ( PTGX ), the Wall Street Journal reported on Friday, citing people familiar with the matter.

A deal is not guaranteed and the exact details being discussed could not be learned, the newspaper said.

The two companies are already working together on an oral treatment for immune diseases such as plaque psoriasis and ulcerative colitis.

J&J holds exclusive rights to sell the drug and owns nearly 4% of Protagonist's shares, according to FactSet, the report said.

The companies did not immediately respond to Reuters' requests for comment.

(Reporting by Kamal Choudhury in Bengaluru; Editing by Anil D'Silva and Tasim Zahid)