IL15 and rheumatoid arthritis: Soluble IL-15 was not detected in coculture supernatants; in addition, very low amounts of soluble BAFF were present, and exogenous rhBAFF could not halt B cell apoptosis at concentrations below 10 ng/ml, consistent with previous work supporting the necessity of direct cell contact for the effect of BAFF expressed on RASFib to take place [12], [13].Peripheral blood B cells from RA patients have been shown to display several specific features [37]–[39] indicative of a preactivated state.