The monoclonal antibody ER-BMDM1 recognizes a macrophage and dendritic cell differentiation antigen with aminopeptidase activity

Abstract Here we describe the reactivity of monoclonal antibody (mAb) ER-BMDM1, directed against a 160-kDa cell membrane-associated antigen (Ag) with aminopeptidase activity. The aminopeptidase recognized by ER-BMDM1 is present on various mouse macrophage (MΦ) and dendritic cell (DC) subpopulations as well as on microvillous epithelia. Analysis of ER-BMDM1 Ag expression in in vitro models of MΦ maturation revealed that the Ag is expressed at increasing levels upon maturation of MΦ. In vivo, high level expression of the ER-BMDM1 Ag occurs after thmonocytic stage of maturation, since bone marrow cells and peripheral blood monocytes are essentially ER-BMDM1 negative. Analysis of isolated-resident and elicited MΦ populations showed that ER-BMDM1 recognizes a specific subpopulation of mature MΦ: only some resident peritoneal and alveolar MΦ are ER-BMDM1 positive, whereas virtually all thioglycollate-elicited peritoneal exudate MΦ bind the mAb. In lymphoid organs, a subpopulation of MΦ is recognized as well as interdigitating cells (IDC) located in T cell areas. Phenotypic analysis of isolated DC- the in vitro equivalents of IDC - from spleen and lymph nodes confirmed that the majority of this important antigen-presenting cell population expresses the ER-BMDM1 aminopeptidase. The molecular characteristics of the ER-BMDM1 Ag suggest that it may represent the mouse homolog of human CD13

A Conduit System Distributes Chemokines and Small Blood-borne Molecules through the Splenic White Pulp

Access to the splenic white pulp is restricted to lymphocytes and dendritic cells. Here we show that movement of molecules from the blood into these confined areas is also limited. Large molecules, such as bovine serum albumin (68 kD), immunoglobulin G (150 kD), and 500 kD dextran are unable to enter the white pulp, whereas smaller blood-borne molecules can directly permeate this compartment. The distribution is restricted to a stromal network that we refer to as the splenic conduit system. The small lumen of the conduit contains collagen fibers and is surrounded in the T cell areas by reticular fibroblasts that express ER-TR7. It also contains the chemokine CCL21. Conversely, in B cell follicles the B cell–attracting chemokine CXCL13 was found to be associated with the conduit and absence of ER-TR7+ fibroblasts. These results show heterogeneity of reticular fibroblasts that enfold the conduit system and suggest that locally produced chemokines are transported through and presented on this reticular network. Therefore, the conduit plays a role in distribution of both blood-borne and locally produced molecules and provides a framework for directing lymphocyte migration and organization of the splenic white pulp

Regulation of fucosyltransferase-VII expression in peripheral lymph node high endothelial venules

Binding of L-selectin to the highly glycosylated peripheral lymph node addressins (PNAd) plays a central role in the normal recirculation of lymphocytes between the bloodstream and the lymph node. This interaction requires correct fucosylation of the PNAd, mediated by the recently identified fucosyltransferase-VII (Fuc-TVII). Here we show that during ontogeny Fuc-TVII is absent at the day of birth, barely detectable on day 1, and clearly present from day 2 onwards. PNAd expression as detected by the MECA-79 antibody precedes the expression of Fuc-TVII. Furthermore, we demonstrate that in adult mice antigenic stimulation of peripheral lymph nodes leads to a temporary disappearance of Fuc-TVII at days 2 and 3 after stimulation, followed by a complete reappearance by day 4, while expression of MECA-79 is never completely absent during this period. Finally, occlusion of afferent lymphatics to peripheral lymph nodes resulted in a decreased expression of Fuc-TVII in the high endothelial venules by day 5, and complete disappearance within 8 days. We conclude that the activity of Fuc-TVII in cells of high endothelial venules is directly affected by afferent lymph and activation processes that occur in the lymph node after antigenic stimulation. The expression of Fuc-TVII is therefore yet another level at which the function of high endothelial venules, and thus lymphocyte trafficking, can be regulated.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/48706/1/3040_ftp.pd

SIRP alpha on Mouse B1 Cells Restricts Lymphoid Tissue Migration and Natural Antibody Production

The inhibitory immunoreceptor SIRPα is expressed on myeloid and neuronal cells and interacts with the broadly expressed CD47. CD47-SIRPα interactions form an innate immune checkpoint and its targeting has shown promising results in cancer patients. Here, we report expression of SIRPα on B1 lymphocytes, a subpopulation of murine B cells responsible for the production of natural antibodies. Mice defective in SIRPα signaling (SIRPαΔCYT mice) displayed an enhanced CD11b/CD18 integrin-dependent B1 cell migration from the peritoneal cavity to the spleen, local B1 cell accumulation, and enhanced circulating natural antibody levels, which was further amplified upon immunization with T-independent type 2 antigen. As natural antibodies are atheroprotective, we investigated the involvement of SIRPα signaling in atherosclerosis development. Bone marrow (SIRPαΔCYT>LDLR−/−) chimaeric mice developed reduced atherosclerosis accompanied by increased natural antibody production. Collectively, our data identify SIRPα as a unique B1 cell inhibitory receptor acting to control B1 cell migration, and imply SIRPα as a potential therapeutic target in atherosclerosis

New insights into the cell biology of the marginal zone of the spleen

In the marginal zone of the spleen the bloodstream passes through an open system of reticular cells and fibers in which various myeloid and lymphoid cells are located. Macrophages in this region are well equipped to recognize pathogens and filter the blood by virtue of unique combinations of pattern recognition receptors. They interact with a specific set of B cells that can be found only in the marginal zone and that are able to react rapidly to bacterial antigens in particular. This combination of strategically located cells is an important factor in our defense against blood-borne pathogens. New data on the development of the marginal zone itself and the marginal zone B cells are reviewed and discussed in light of the function of the spleen in host defense

The role of CD45+CD4+CD3- cells in lymphoid organ development

In the last 10 years the continuing search for gene function has yielded many mutant mice that unexpectedly showed a complete lack of lymph nodes and/or Peyer's patches. With the realization that all these functionally highly diverse genes are involved at some point in the development of lymphoid organs, the challenge now is to assign a function to the molecules involved in lymphoid organ development. It will be important to determine the sequence of molecular events and assign this to the cellular events that lead to an accumulation of hematopoietic cells in one location, ultimately forming an organized lymphoid organ. Here we will focus on CD45+CD4+CD3- cells that are the early colonizing cells in lymph nodes and Peyer's patches and develop a hypothetical model of their contribution to the creation of organized lymphoid structures

A function for the macrophage F4/80 molecule in tolerance induction

The F4/80 monoclonal antibody has been used widely as a marker for mouse macrophages. The antigen (Ag) recognized by the antibody has been characterized as a member of the epidermal growth factor (EGF)-transmembrane 7 (TM7) family, although the function of the molecule has remained elusive. A recent study provides evidence for a role of the F4/80 molecule in the induction of immunological tolerance. This study appears to provide clear evidence for a role of the F4/80 molecule in the immune system, however, what does it really tell us about the activities of the F4/80 molecule

Development and function of the splenic marginal zone

The marginal zone of the spleen is a crucial region where blood-borne pathogens are sequestered by macrophages with unique arrays of scavenger molecules. In addition, a special population of B cells, which is capable of rapid activation, resides in this region. Marginal zone B cells and macrophages together form an efficient interplay between innate and adaptive immunity. The developmental pathways that lead to the formation of the marginal zone are described, and the function of the marginal zone is discussed in relation to the function of the spleen as the major blood-filtering organ of the bod