CD36 IS RAPIDLY AND TRANSIENTLY UP-REGULATED 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 bl ood lymphocytes (PBL) following mitogenic stimulation. CD36, scarcely expressed on resting cell membranes, was rapidly upregulated on PBL af ter 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 inhibitio n of protein synthesis by cycloheximide did not modify the PHA-induced expression of CD36. Neither the anti-CD3 OKT3 mAb nor the anti-CD2 BI L 2.29 and 9.1 mAbs induced any significant upregulalion of the molecu le. 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 expres sion. The phorbol-2-myristate-13-acetate (PMA), alone or in combinatio n with ionomycin, was unable to activate the expression of CD36, while it inhibited the PKA-induced upregulation, The PHA-induced upregulati on of CD36 was partially inhibited by the addition of LY294002 or wort mannin, while not affected by that of calphostin C. Thus, CD36 was fou nd to be early and transiently upregulated by PKA stimulation on PBL. The rapid modulation of the molecule was not related to new protein sy nthesis, but was probably due to the insertion into the plasma membran e of a presynthetized protein pool.