CD36 is rapidly and transiently upregulated on phytohemagglutinin (PHA)‐stimulated peripheral blood lymphocytes. Analysis by a new monoclonal antibody (UN7)

The monoclonal antibody (mAb) UN7, clustered as an anti-CD36 mAb, has been used to test the cell surface expression of CD36 on peripheral blood lymphocytes (PBL) following mitogenic stimulation. CD36, scarcely expressed on resting cell membranes, was rapidly upregulated on PBL after phytohemagglutinin (PHA) stimulation. The antigen was detected on the cell surface after 15 min of stimulation, increased rapidly by 60 min and peaked between 3 and 12 h, declining thereafter. The inhibition of protein synthesis by cycloheximide did not modify the PHA-induced expression of CD36. Neither the anti-CD3 OKT3 mAb nor the anti-CD2 BIL 2.29 and 9.1 mAbs induced any significant upregulation of the molecule. The addition of anti-CD28 15E8 mAb or IL-2 or IFN-gamma to PHA or anti-CD3 or anti-CD2 mAbs did not influence the pattern of CD36 expression. The phorbol-2-myristate-13-acetate (PMA), alone or in combination with ionomycin, was unable to activate the expression of CD36, while it inhibited the PHA-induced upregulation. The PHA-induced upregulation of CD36 was partially inhibited by the addition of LY294002 or wortmannin, while not affected by that of calphostin C. Thus, CD36 was found to be early and transiently upregulated by PHA stimulation on PBL. The rapid modulation of the molecule was not related to new protein synthesis, but was probably due to the insertion into the plasma membrane of a presynthetized protein pool.