Phenotypic and functional characterization of CD11c+ dendritic cell population in mouse Peyer's patches

The antigen-presenting cell system in the gastrointestinal tract, one of three main sites (skin and lung being the others) of primary antigen contact, is poorly understood. Our study focused on dendritic cells (DC) as possible candidates for antigen uptake, processing and presentation in mucosal inductive sites, such as Peyer's patches (PP). To investigate the morphology, immunophenotype and stimulatory activity of intestinal DC, a procedure was developed to obtain a cell population by using collagenase digestion of PP, density centrifugation and cell sorting on the basis of CD11c expression. The resultant low-density cell fraction consisted of a nonadherent cell population expressing different intensities of CD11c that could at least be characterized by typical DC morphology (e.g. abundant cytoplasma with veil-like cytoplasmatic dendrites, irregularly shaped nuclei, multivesicular and multilamellar bodies), constitutive levels of surface MHC class II, the presence of macrophage-specific markers, such as F4/80, Mac-I and Fc receptors, respectively, on subpopulations of CD11c⁺ sorted cells and expression of adhesion and co-stimulatory receptors like ICAM-1 and CD44. The capability of this low-density CD11c⁺ fraction to stimulate T cell responses was demonstrated in primary allogeneic mixed-lymphocyte reactions (MLR). Herein, we show that the freshly isolated CD11c⁺ cells showed weak accessory function, but develop this capacity following short-term culture in vitro in the presence of granulocyte/macrophage colony-stimulating factor. Although the nature and functional capacity of the isolated CD11c⁺ needs further clarification, these preliminary results describing phenotype and accessory function provide some evidence that these cells isolated from the PP may be immature forms of DC and play a crucial role as antigen-presenting cells with important implications for understanding the complex network regulating intestinal antigen uptake, processing and presentation.