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J. Exp. Med.,
Volume 188, Number 11, December 7, 1998 2019-2031
By
From the TVW Telethon Institute for Child Health Research (affiliated with the University of
Western Australia), West Perth, Western Australia 6872, Australia
Consistent with their role in host defense, mature dendritic cells (DCs) from central lymphoid
organs preferentially prime for T helper cell type 1 (Th1)-polarized immunity. However, the "default" T helper response at mucosal surfaces demonstrates Th2 polarity, which is reflected in
the cytokine profiles of activated T cells from mucosal lymph nodes. This study on rat respiratory tract DCs (RTDCs) provides an explanation for this paradox. We demonstrate that freshly
isolated RTDCs are functionally immature as defined in vitro, being surface major histocompatibility complex (MHC) II lo, endocytosishi, and mixed lymphocyte reactionlo, and these
cells produce mRNA encoding interleukin (IL)-10. After ovalbumin (OVA)-pulsing and
adoptive transfer, freshly isolated RTDCs preferentially stimulated Th2-dependent OVA-specific immunoglobulin (Ig)G1 responses, and antigen-stimulated splenocytes from recipient animals produced IL-4 in vitro. However, preculture with granulocyte/macrophage colony stimulating factor increased their in vivo IgG priming capacity by 2-3 logs, inducing production of
both Th1- and Th2-dependent IgG subclasses and high levels of IFN-
by antigen-stimulated splenocytes. Associated phenotypic changes included upregulation of surface MHC II and B7
expression and IL-12 p35 mRNA, and downregulation of endocytosis, MHC II processing-
associated genes, and IL-10 mRNA expression. Full expression of IL-12 p40 required additional signals, such as tumor necrosis factor
or CD40 ligand. These results suggest that the observed
Th2 polarity of the resting mucosal immune system may be an inherent property of the resident DC population, and furthermore that mobilization of Th1 immunity relies absolutely on
the provision of appropriate microenvironmental costimuli.
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