Enhancement of murine B cell responses to lipopolysaccharide by supernatants of irradiated peripheral blood leukocytes.

At low cell density, the proliferative response of B cells to lipopolysaccharide (LPS) is not detectable. We investigated under these experimental conditions the role of several cell populations on the LPS-induced B-cell proliferation. The addition to murine B cells of irradiated peripheral blood leukocytes (PBL) from the C3H/HeJ mouse strain, or of culture supernatants of these cells, efficiently restored a response to LPS. Similar results were also obtained with irradiated PBL from other mouse strains and from rabbits. The activities of the culture supernatants were not significantly modified when the PBL were depleted of adherent cells or of Thy-1.2 positive cells, thus suggesting that the active factors were secreted neither by T cells, nor by monocytes.