Comparison of mycoplasma(s)-derived B cell mitogenic activity with lipopolysaccharide.

Culture fluid (CF) from LA cells (LA-CF) strongly stimulated the proliferation of normal A/J mouse spleen cells in vitro. This activity was nondialyzable, labile to 56 degrees C for 20 min., sedimentable, H-2 and species unrestricted, and was found to be mycoplasma-derived. LA-CF was active for B cells because in vitro treatment of A/J spleen cells with anti mouse Ig antiserum and complement eliminated their responsiveness to LA-CF. LA-CF stimulated the resting, small spleen cells of the nude mouse as strongly as lipopolysaccharide (LPS) did. Spleen cells of the X chromosome-linked immunodeficiency (Xid) mouse were stimulated by LPS to a half of the control mice, and by LA-CF to a quarter of the control. LPS-low responder (C3H/HeJ) spleen cells were also stimulated by LA-CF. The mycoplasma(s)-derived B cell mitogen in the LA-CF was different from LPS.