Isolation of human intrahepatic leukocytes for phenotypic and functional characterization by flow cytometry

With the growing appreciation of tissue-resident immunity, studying tissue-specific immune cells contributing to both homeostasis and disease is imperative. Here, we provide a protocol for the isolation of human intrahepatic leukocytes (IHL) maximizing viability, purity, and yield. Our protocol is scalable by tissue weight, allowing for reproducible and efficient IHL liberation suitable for functional characterization, cell isolation, and profiling by flow (or mass) cytometry. Furthermore, we provide a "guide" to determine an expected IHL yield per gram of tissue processed. For complete details on the use and execution of this protocol, please refer to Stegmann et al. (2016), Pallett et al. (2017), Easom et al. (2018), Swadling et al. (2020), Pallett et al. (2020), and Zakeri et al. (2022).

Natural Killer Cells in Liver Disease

Natural killer (NK) cells comprise one of the most abundant immune cell populations in human liver and the nature and functions of these cells have been a focus of recent interest. Here, we consider the possible roles of NK cells in diverse liver diseases, concentrating on data from patient studies. NK cells can be protective, killing virally infected and cancerous cells in the liver and limiting fibrosis by eliminating hepatic stellate cells. However, they can also be deleterious, contributing to pathology in viral hepatitis by killing hepatocytes and downregulating virus-specific T-cell responses. It has recently emerged that a large fraction of hepatic NK cells constitute a distinct liver-resident subset and we highlight the need to distinguish between circulating and liver-resident NK cells in future studies. There is also a need for further investigation into how NK cells are influenced by the liver microenvironment and what scope there is to harness their immunotherapeutic potential.

T Cells Infiltrating Diseased Liver Express Ligands for the NKG2D Stress Surveillance System

NK cells, which are highly enriched in the liver, are potent regulators of antiviral T cells and immunopathology in persistent viral infection. We investigated the role of the NKG2D axis in T cell/NK cell interactions in hepatitis B. Activated and hepatitis B virus (HBV)-specific T cells, particularly the CD4 fraction, expressed NKG2D ligands (NKG2DL), which were not found on T cells from healthy controls (p < 0.001). NKG2DL-expressing T cells were strikingly enriched within HBV-infected livers compared with the periphery or to healthy livers (p < 0.001). NKG2D⁺NK cells were also increased and preferentially activated in the HBV-infected liver (p < 0.001), in direct proportion to the percentage of MICA/B-expressing CD4 T cells colocated within freshly isolated liver tissue (p < 0.001). This suggests that NKG2DL induced on T cells within a diseased organ can calibrate NKG2D-dependent activation of local NK cells; furthermore, NKG2D blockade could rescue HBV-specific and MICA/B-expressing T cells from HBV-infected livers. To our knowledge, this is the first ex vivo demonstration that non-virally infected human T cells can express NKG2DL, with implications for stress surveillance by the large number of NKG2D-expressing NK cells sequestered in the liver.

Mass, charge, and subcellular localization of a unique secretory product identified by the basophil-specific antibody BB1

BACKGROUND

BB1 is a basophil-specific mAb (Lab Invest 1999;79:27-38). The identity of the corresponding antigen has not been determined, but it gives a granular appearance on staining and is secreted on activation of basophils.

OBJECTIVE

We sought to further characterize the basophilspecific antigen identified by BB1.

METHODS

Intracellular localization was determined by flow cytometry and by immunogold labeling and electron microscopy. Physical chemical properties were investigated by gel filtration chromatography and preparative isoelectric focusing.

RESULTS

In flow cytometry, permeabilization of cells increased immunofluorescence 100-fold, confirming the predominantly intracellular localization of the antigen. It was further localized to the secretory granules by immunoelectron microscopy. Double labeling with a CD63-specific antibody demonstrated selective binding of BB1 to the granule matrix. Gel filtration chromatography indicated that the antigen is secreted as a complex of approximately 5 x 10(6) d, which was well resolved from the 210-kd supramolecular complex containing tryptase. The antigen was degraded by pronase. Isoelectric focusing indicated a highly basic protein with an isoelectric point of 9.6.

CONCLUSION

With its granule localization, release on cell activation, and unique properties, the antigen identified by BB1 could be a novel mediator of allergic disease. We propose the name basogranulin for this novel basophil-specific protein.