FC ALPHA-RECEPTOR EXPRESSION ON THE MYELOMONOCYTIC CELL-LINE THP-1 - COMPARISON WITH HUMAN ALVEOLAR MACROPHAGES

Immunoglobulin A (IgA) and alveolar macrophages are two important comp onents of the immune system in the respiratory tract. Fc alpha-recepto rs (FcalphaR) are present on neutrophils, eosinophils and a series of human mononuclear phagocytes, including monocytes, alveolar macrophage s and leukaemia cell lines (U-937). In the present study, using idioty pes and anti-idiotypic antibodies, we report that THP-1 cells, a myelo monocytic cell line, constitutively express FcalphaR and that all IgA preparations used bind the receptor. Of the stimuli used (phorbol myri state acetate, retinoic acid, calcitriol), only calcitriol can induce differentiation of THP-1 cells, as assessed by CD14 expression. The ex pression of FcalphaR appears to be independent of cell differentiation , since calcitriol pretreatment has no effect on IgA-binding. Finally, My43, a monoclonal antibody recognizing the FcalphaR on U-937 cells, does not bind to THP-1 cells or to human alveolar macrophages. In addi tion, preincubation of THP-1 cells or human alveolar macrophages with My43 does not diminish IgA-binding to these cells. Ribonucleic acid (R NA) encoding the FcalphaR isolated from U-937 is expressed, although p ossibly at a lower level, in alveolar macrophages and THP-1 cells. In conclusion, FcalphaR are constitutively expressed on THP-1 cells and s hare some characteristics with the FcalphaR described in human alveola r macrophages. THP-1 cells, therefore, may represent a reasonable mode l for further investigation of the interaction of immunoglobulin A and tissue macrophages.