Physiological Role of Macrophage Inflammatory Protein-3α Induction during Maturation of Intestinal Macrophages

Abstract

Intestinal macrophages (IMAC) are a central component in the defense of the intestinal mucosa against luminal microbes. In normal mucosa, monocytes differentiate to immunologically tolerant IMAC with a typical phenotype lacking activation markers such as CD14 and TLRs 2 and 4. CD33+ IMAC were isolated from normal intestinal mucosa by immunomagnetic beads. A subtractive hybridization subtracting mRNA from normal IMAC from those of in vitro differentiated macrophages was performed. IMAC differentiation was studied in multicellular spheroids (MCS). Functional assays on migration of CD45R0+ T cells were performed in MCS coculture models. Of 76 clones, 3 obtained by subtractive mRNA hybridization showed >99% homology to mRNA of MIP-3α, indicating that this chemokine is induced in IMAC compared with in vitro differentiated macrophages. MIP-3α protein expression was confirmed in cryostat sections of normal intestinal mucosa by immunohistochemistry. IMAC in the lamina propria stained positive for MIP-3α. FACS of purified IMAC clearly indicated expression of MIP-3α in these cells. In the MCS-in vitro differentiation model for IMAC, MIP-3α protein expression was absent on day 1 but detectable on day 7 of coculture, demonstrating the induction of MIP-3α during differentiation of IMAC. IMAC attracted CD45R0+ T cells to migrate into an MCS coculture model. In human mucosa, a close contact between IMAC and CD45R0+ T cells could be demonstrated. MIP-3α is induced during the differentiation of monocytes into IMAC. Our data suggest that MIP-3α expression could be involved in the recruitment of CD45R0+ cells into the lamina propria.

MIP-3α Expression in Macrophages Is NOD Dependent

“…Increased MIP-3α protein secretion was confirmed by ELISA. In vivo, MIP-3α protein expression in human intestinal epithelial cells and IMACs was determined in a nonquantitative manner by immunohistochemistry and flow cytometry [31]. In this work, we could confirmMIP-3α mRNA expression ex vivo in freshly isolated intestinal epithelial cells and IMACs.…”

“…Other cell types, such as endothelial cells, fibroblasts, and monocytes are also known to express MIP-3α [28,30]. High MIP-3α mRNA and protein expression are induced during the specific differentiation of IMACs as shown in previous studies from our laboratory [31]. Similarly, MIP-3α mRNA was found to be highly expressed in differentiated macrophages in the lung [28].…”

“…These data suggest that CCR6 functions on memory T cells that home to mucosal sites as part of an immune response [26]. Professional antigen-presenting and MIP-3α-secreting IMACs may serve as a contact point for CD45R0 + memory T and B cells and subpopulations of DCs [31]. …”

Recruitment of CCR6-expressing Th17 cells by CCL20 secreted from plasmin-stimulated macrophages

“…Under inflammatory conditions, epithelial cells [31], endothelial cells, fibroblasts, and monocytes are thought to be important sources of CCL20 production [16,32]. Similarly, some studies have shown that high expression of CCL20 is induced in differentiated macrophages in intestinal epithelium [33] and lung [32]. In human inflamed pulp sections, CCL20 is mostly expressed by macrophages accumulated in the area adjacent to carious lesions and CCR6 expression is also elevated in inflammatory infiltrating lymphocytes, which suggest that CCL20 may play a major role in the advancement of pulpal inflammation via the recruitment of CCR6-expressing lymphocytes [34].…”

The Innate Immune System: A Trigger for Many Chronic Inflammatory Intestinal Diseases

“…In IBD this differentiation is altered at sites of inflammation [16,17,18,19,20,21,22,23]. A different phenotype with different functional properties occurs [16,17,18,19,20,21,22,23,24]. …”