THE HUMAN MONOCYTE-LIKE CELL-LINE THP-1 EXPRESSES FC-GAMMA-RI AND FC-GAMMA-RII

THP-1 cells are a monocyte-like cell line derived from a patient with acute monocytic leukemia and unlike other leukemic cell lines has a normal diploid karyotype. We have characterized Fc-gamma-R expression on this cell line by flow cytometry, radiolabeled IgG1 and monoclonal antibody (mAb) binding assays, and biochemical analysis. Flow cytometric analysis of THP-1 cells with anti-Fc-gamma-RI, II, and III mAb, and a rabbit anti-Fc-gamma-RIII F(ab')2 demonstrated that only Fc-gamma-RI and Fc-gamma-RII are expressed by these cells. A panel of anti-Fc-gamma-RIII mAb (anti-CD16) failed to bind to THP-1 cells. Biochemical studies identified polypeptides of 64 to 78 kDa (Fc-gamma-RI) and of 42 to 53 kDa (Fc-gamma-RII). Fc-gamma-R expression was determined by binding of radioiodinated human IgG1 (to detect Fc-gamma-RI), mAb IV.3 (to detect Fc-gamma-RII), or rabbit IgG immune complexes. Thirty-five thousand high affinity binding sites (dissociation constant [K(D)] = 4.22 x 10(-9M) for IgG1 were found on THP-1 cells. Interferon-gamma (IFN-gamma) upregulated Fc-gamma-RI expression by THP-1 cells 2.8-fold, whereas Fc-gamma-RI on U937 cells was increased six- to eight-fold by this cytokine. Phorbol myristate acetate (PMA), tumor necrosis factor-alpha (TNF-alpha), and vitamin D3 had no effect on IgG1 binding by THP-1 cells. Fifty thousand IgG molecules in immune complexes bound to THP-1 cells. IFN-gamma treatment increased this binding by four-fold, PMA treatment resulted in a 50% increase in the number of IgG immune complexes bound, whereas vitamin D3 treated THP-1 cells bound half as many IgG immune complexes as control cells. Binding assays utilizing mAb IV.3 identified 50,000 sites per cell. Treatment of THP-1 cells with IFN-gamma, TNF-alpha, PMA, or vitamin D3 had no effect on Fc-gamma-RII expression. That Fc-gamma-RI plays a predominant role in immune complex binding was demonstrated by inhibition studies. Human IgG1 as well as mouse IgG2a mAb to Fc-gamma-RII inhibited immune complex binding by 76 to 84%, whereas mouse IgG1 mAb to Fc-gamma-RII had minimal effect on immune complex binding. Fc-gamma-R expression may not be linked to differentiation of THP-1 cells since only 1,25 vitamin D3 was able to induce the expression of CD14, a marker of mature monocytic phenotype.