 The principle is based on the secretion of antibody from "in vivo" activated plasma B cells found in blood circulation for a short period of time in response to TB-antigens during active TB infection rather than latent TB infection.PBMCs were separated from blood on Ficoll-Paque by differential centrifugation and were suspended in 24-well tissue culture plates culture medium.Different dilutions of PBMCs were incubated at 37 °C with 5% CO2.