Sensitized lymphocytes from 3 cows vaccinated with Anaplasma antigen were isolated and reacted, in vitro with antigen in a microculture lymphocyte transformation test. The addition of 2-mercaptoethanol at a concentration of 25 .mu.l of 4 .times. 10-3 M solution/well significantly (P .ltoreq. 0.01) increased [3H]thymidine incorporation compared to microculture without 2-mercaptoethanol.