Protein I and protein II from the outer membrane of Escherichia coli are mouse B-lymphocyte mitogens.

Protein I from the outer membrane of Escherichia coli is a B-lymphocyte mitogen in mice. Polyclonal activation of mouse splenocytes was demonstrated by 3H-thymidine incorporation into DNA, 3H-uridine incorporation into RNA, and by a hemolytic plaque assay in three inbred mouse strains. B-lymphocytes from LPS responder mice (C57Bl/10, STU/nu/nu) and LPS non-responder mice (C3H/HeJ) both responded well to protein I. The presence of serum was not necessary for mitogenicity; bovine serum albumin exhibited a beneficial effect on serum-depleted cultures. Thymocytes of C3H/HeJ mice were not activated by protein I. Protein II* from E. coli was also tested in our systems and showed a weak B-lymphocyte stimulatory activity. Human peripheral blood lymphocytes were not activated.