The human monocyte-like cell line THP-1 expresses FcγRI and FcγRII

Abstract

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 FcγR 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-FcγRI, II, and III mAb, and a rabbit anti-FcγRIII F(ab')2 demonstrated that only FcγRI and FcγRII are expressed by these cells. A panel of anti-FcγRIII mAb (anti-CD16) failed to bind to THP-1 cells. Biochemical studies identified polypeptides of 64 to 76 kDa (FcγRI) and of 42 to 53 kDa (FcγRII). FcγR expression was determined by binding of radioiodinated human IgG1 (to detect FcγRI), mAb IV.3 (to detect FcγRII), 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-γ (IFNγ) upregulated FcγRI expression by THP-1 cells 2.8-fold, whereas FcγRI on U937 cells was increased six- to eight-fold by this cytokine. Phorbol myristate acetate (PMA), tumor necrosis factor-α (TNFα), 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. IFNγ 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 IFNγ, TNFα, PMA, or vitamin D3 had no effect on FcγRII expression. That FcγRI plays a predominant role in immune complex binding was demonstrated by inhibition studies. Human IgG1 as well as mouse IgG2a mAb to FcγRII inhibited immune complex binding by 76 to 84%, whereas mouse IgG1 mAb to FcγRII had minimal effect on immune complex binding. FcγR 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.