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Professional phagocytosis in mammals is considered to be performed exclusively by myeloid cell types. In this study, we demonstrate, for the first time, that a mammalian lymphocyte subset can operate as a professional phagocyte. By using confocal microscopy, transmission electron microscopy, and functional Ag presentation assays, we find that freshly isolated human peripheral blood gammadelta T cells can phagocytose Escherichia coli and 1 microm synthetic beads via Ab opsonization and CD16 (FcgammaRIII), leading to Ag processing and presentation on MHC class II. In contrast, other CD16(+) lymphocytes, i.e., CD16(+)/CD56(+) NK cells, were not capable of such functions. These findings of distinct myeloid characteristics in gammadelta T cells strongly support the suggestion that gammadelta T cells are evolutionarily ancient lymphocytes and have implications for our understanding of their role in transitional immunity and the control of infectious diseases and cancer.
Wu et al. (Tue,) studied this question.