Published online before print March 9, 2005

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(Journal of Leukocyte Biology. 2005;77:1008-1017.)
© 2005 by Society for Leukocyte Biology

Aminopeptidase N (CD13) functionally interacts with FcRs in human monocytes

Department of Immunology, Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México

¹Correspondence: Departamento de Inmunología, Instituto de Investigaciones Biomédicas, UNAM, Circuito Escolar, S/N Ciudad Universitaria, México D.F., C.P. 04510 Mexico. E-mail: ortsoto{at}servidor.unam.mx

Aminopeptidase N (E.C. 3.4.11.2) is a membrane-bound metalloproteinase expressed in many tissues. Although its cytoplasmic portion has only eight amino acids, cross-linking of CD13 by monoclonal antibodies (mAb) has been shown to trigger intracellular signaling. A functional association between CD13 and receptors for immunoglobulin G (FcRs) has been proposed. In this work, we evaluated possible functional interactions between CD13 and FcRs in human peripheral blood monocytes and in U-937 promonocytic cells. Our results show that during FcR-mediated phagocytosis, CD13 redistributes to the phagocytic cup and is internalized into the phagosomes. Moreover, modified erythrocytes that interact with the monocytic cell membrane through FcRI and CD13 are ingested simultaneously, more efficiently than those that interact through the FcRI only. Also, co-cross-linking of CD13 with FcRI by specific mAbs increases the level and duration of Syk phosphorylation induced by FcRI cross-linking. Finally, FcRI and CD13 colocalize in zones of cellular polarization and coredistribute after aggregation of either of them. These results demonstrate that CD13 and FcRI can functionally interact on the monocytic cell membrane and suggest that CD13 may act as a signal regulator of FcR function.

Key Words: Fc receptors • macrophages • phagocytosis

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