Characterization of a new human macrophage cell line 2MAC. 1. Expression of functional macrophage CD16 (Fc gammaRIIIA/gamma) and tissue factor induction on ligation of HLA-DR

Discovering Molecules That Regulate Efferocytosis Using Primary Human Macrophages and High Content Imaging

Defective clearance of apoptotic cells can result in sustained inflammation and subsequent autoimmunity. Macrophages, the “professional phagocyte” of the body, are responsible for efficient, non-phlogistic, apoptotic cell clearance. Controlling phagocytosis of apoptotic cells by macrophages is an attractive therapeutic opportunity to ameliorate inflammation. Using high content imaging, we have developed a system for evaluating the effects of antibody treatment on apoptotic cell uptake in primary human macrophages by comparing the Phagocytic Index (PI) for each antibody. Herein we demonstrate the feasibility of evaluating a panel of antibodies of unknown specificities obtained by immunization of mice with primary human macrophages and show that they can be distinguished based on individual PI measurements. In this study ~50% of antibodies obtained enhance phagocytosis of apoptotic cells while approximately 5% of the antibodies in the panel exhibit some inhibition. Though the specificities of the majority of antibodies are unknown, two of the antibodies that improved apoptotic cell uptake recognize recombinant MerTK; a receptor known to function in this capacity in vivo. The agonistic impact of these antibodies on efferocytosis could be demonstrated without addition of either of the MerTK ligands, Gas6 or ProS. These results validate applying the mechanism of this fundamental biological process as a means for identification of modulators that could potentially serve as therapeutics. This strategy for interrogating macrophages to discover molecules regulating apoptotic cell uptake is not limited by access to purified protein thereby increasing the possibility of finding novel apoptotic cell uptake pathways.

MHC class II molecules activate NFAT and the ERK group of MAPK through distinct signaling pathways in B cells

MHC class II (MHC-II) molecules are capable of transducing signals with the help of associated molecules. Although the search to find associated molecules over the past few years has been fruitful, it remains clear that not all signaling components and their mechanisms of action have been identified. In this study, we investigated calcium and MAPK signaling pathways using the BJAB and Raji human B cell lines. We demonstrate that calcium mobilization is an isotype-independent event that triggers the dephosphorylation of NFAT. We also show that BCR activation followed by MHC-II ligation increases the activation of NFAT. This signaling pathway differs from MHC-II-mediated MAP activation, where MEK1/2 and ERK1/2 phosphorylation are isotype-specific events, which correspond to the induction of c-Fos and formation of AP-1. Future studies should elucidate the intertwined, intricate signaling cascades triggered by BCR and MHC-II leading to humoral immune responses.

Functional and biochemical characterization of a novel human macrophage-derived negative regulator of haematopoiesis

It is believed that haematopoiesis is regulated by both positive and negative signals derived from the marrow microenvironment, which includes macrophages. The identity and mechanism of action of the proteins mediating negative regulation is an area of active investigation. We report here the identification and initial characterization of a novel suppressor of early haematopoietic progenitors, designated NRH (for Negative Regulator of Haematopoiesis), isolated from the recently established human macrophage line 2MAC. The mechanism of NRH suppression appears to involve a marked decrease in the cycling of early progenitor cells. NRH activity was shown to be reversible and to correspond to an acidic, heparin-binding glycoprotein with a molecular weight of approximately 20 000 daltons ( approximately 20 kDa). By exploiting lectin specificity, hydrophobic interaction, and heparin affinity, we have developed a procedure for the rapid isolation of highly purified NRH from 2MAC-conditioned medium. By a number of functional and biochemical criteria, NRH appears to represent a novel macrophage-derived negative regulator of haematopoiesis which may have future application in certain clinical settings as a chemoprotectant of primitive haematopoietic cells.

Cytokine modulatable signalling through macrophage HLA class II. 1. IFN-gamma upregulates the efficiency of Ca2+ mobilization in response to ligation of macrophage HLA-DP

The human macrophage line 2MAC, established recently from peripheral blood, expresses a number of lineage-specific markers as well as a broad array of intercellular adhesion molecules, including high levels of HLA class I and class II. We have presented evidence elsewhere that 2MAC can be productively applied to the study of signal transduction through macrophage HLA class II. Namely, we showed that ligation of 2MAC HLA class II, but not HLA class I, by monoclonal antibody (mAb) elicits an increase in free cytoplasmic Ca2+ concentration [Ca2+]i. Moreover, this Ca2+ flux appears to be functionally relevant: ligation of HLA-DR, but not HLA class I, by mAb results in the Ca2+ mobilization-dependent induction of tissue factor, the high-affinity cellular receptor for factor VII/VIIa. Here we show that 2MAC is uniquely valuable for addressing the efficiency of signal transduction through HLA class II. Namely, we show here that prior culture of 2MAC cells with interferon-gamma (IFN-gamma) profoundly upregulates subsequent Ca2+ mobilization in response to ligation of HLA-DP in the absence of increased cell surface HLA-DP expression. Because IFN-gamma has no effect on 2MAC HLA-DP expression, IFN-gamma must upregulate Ca2+ mobilization by increasing the efficiency of signal transduction through HLA class II (HLA-DP), by targeting some other component of the macrophage HLA class II signalling pathway.