Effects of recombinant interferon-gamma on HLA-DR antigen shedding by human peripheral blood adherent mononuclear cells

CD13 and CD10 expression of granulocytes as markers for the functioning of the immune system: quantification of the expression of membrane molecules using 1:1 labeled monoclonal antibodies and flow cytometry

HLA-DR expression on monocytes as a marker for the functioning of the immune system is known to be severely depressed in immunodeficiency. Up to now, other markers for the function of the immune system are scarce. In the peripheral blood of patients with open heart surgery the expression of the membrane peptidases neprilysin/CD10 and aminopeptidase N/CD13, was determined on granulocytes in comparison to the monocytic HLA-DR expression. We used the QuantiBRITE flow cytometry system, which yields an absolute antigen expression value (antibodies bound per cell) and may be useful in standardizing surface antigen expression analysis. This system makes use of a highly purified phycoerythrin-labeled antibody with a 1:1 fluorochrome-to-protein ratio, and multilevel calibrated beads with known absolute phycoerythrin fluorescence. Our results show that both membrane peptidases on granulocytes show a similar time-course of expression after heart surgery as do HLA-DR molecules on monocytes, with a decrease from days one to three and a subsequent recovery to normal values. In future analyses a possible relationship between the immunodeficiency of patients and a diminished expression of both membrane peptidases on granulocytes has to be investigated.

HLA-DR regulation and the influence of GM-CSF on transcription, surface expression and shedding

Low surface HLA-DR expression is a feature in sepsis. However, the mechanisms that regulate HLA-DR expression have not been elucidated. The current study investigates regulation of HLA-DR gene transcription, post transcriptional events and shedding of surface HLA-DR, as well as the regulation of HLA-DR by GM-CSF and an immunomodulatory cytokine. Plasma and PBMC were collected from septic patients and healthy volunteers. An ELISA was developed to measure soluble HLA. PCR techniques were used to determine HLA-DR mRNA levels, and flow cytometry and fluorescent microscopy were used for measurement of surface expressed and intracellular HLA-DR. Septic patients fulfilling the criteria of the American College of Chest Physicians (ACCP) for sepsis were recruited for the study (n=70). HLA-DR was measured on three consecutive days, days seven and fourteen. Patients were excluded from the study if on immunosuppressive therapy. Results: Higher levels of shed HLA-DR were found in the plasma of septic patients compared to healthy controls. The level of HLA-DR mRNA was significantly lower in septic patients compared to healthy controls, however an increased intracellular HLA-DR expression was observed. When HL-60 cells were treated with GM-CSF, gene transcription, surface expression and shedding of HLA-DR were all up-regulated. These results indicate that the mechanisms involved in the regulation of HLA-DR in sepsis include shedding of HLA-DR from the cell surface and regulation of HLA-DR gene transcription. Post-translational processing of HLA-DR was also seen to be compromised. GM-CSF was shown to regulate HLA-DR at all these levels.

High concentration of soluble HLA-DR in the synovial fluid: generation and significance in "rheumatoid-like" inflammatory joint diseases

In the search for its role in inflammatory joint diseases, soluble HLA-DR (sHLA-DR) was quantitated in 72 synovial fluids (SF) by a newly established immunoenzyme assay. Unlike other soluble receptors which accumulated only moderately (sCD25, sCD4) or negligibly (sHLA class I, sCD8) in the SF, SF sHLA-DR levels exceeded serum levels by up to 3 orders of magnitude and varied disease dependently from "control" values (traumatic synovitis and osteoarthritis: 9.9 +/- 6.1 ng/ml). Clear-cut different SF sHLA-DR values in HLA-DR-associated "rheumatoid-like" (136.5 +/- 130.0 ng/ml) vs HLA-B27-associated "spondylarthropathy-like" arthritic forms (28.4 +/- 29.1 ng/ml) were most significant comparing oligoarticular juvenile chronic arthritis type I (147.6 +/- 112.6 ng/ml) and type II (3.3 +/- 1.1 ng/ml), thus offering a new classification marker. Also ex vivo, large amounts of sHLA-DR were released spontaneously by SF mononuclear cells and found to be related to the T-cell activation state. SF sHLA-DR may be shed in large complexes or micelles, as it eluted mainly at >450 kDa on gel filtration. Western blotting revealed that the majority of SF sHLA-DR consisted of full-length alpha- and beta-chains. Minor fractions of smaller sized antigens seemed to be generated by proteolytic cleavage rather than by alternative splicing, since only minute amounts of HLA-DRB mRNA lacking the transmembrane exon could be amplified by RT-PCR. Distinct forms of high-dose sHLA-DR, able to provoke rather than to suppress T-cell responses, are discussed as contributing to some HLA-DR disease association.

Are soluble monocyte-derived HLA class II molecules candidates for immunosuppressive activity?

Supernatants of human blood monocyte cultures suppressed PHA responses (IL-2 synthesis, IL-2R expression, DNA synthesis) of autologous and allogeneic lymphocytes. The main suppressive activity was found in the 65-kDa (and 23-kDa) range. It could be incompletely neutralized by mAb specific for a non-polymorphic HLA DR determinant and could also be adsorbed to and eluted from an anti-DR immunoabsorbent column. On blots of monocyte lysates and monocyte culture supernatants, the mAb RoDR recognized antigens of nearly the same Mr. The hypothesis that soluble HLA DR alpha beta heterodimers or beta chains are likely candidates for the suppressor factor was confirmed by analogous effects of purified HLA DR molecules. We favor a model in which soluble MHC class II molecules (in contrast to surface-bound ones) may interfere with the association and cross-linking processes necessary for T cell activation by competing for CD4 binding sites.

Enzyme-linked bio-immunoassay for IFN-gamma by HLA-DR induction

A novel enzyme-linked bio-immunoassay (bio-ELISA) has been developed to detect interferon-gamma (IFN-gamma) induced HLA-DR antigen on the surface of human tumor cells. Cells are cultured at 37 degrees C in 96-well microtiter plates in the presence of IFN-gamma for 2 days. After fixation with reagent alcohol the HLA-DR antigen is detected using a monoclonal antibody, followed by goat anti-mouse IgG-HRP conjugate. Four human cell lines were evaluated and all expressed HLA-DR in response to IFN-gamma in a dose-related fashion. Based on sensitivity, reproducibility and absence of antiproliferative effect by IFN-gamma, the COLO 205 cells (colon adenocarcinoma) were determined to be optimal. The bioassay is sensitive to 0.3 ng/ml IFN-gamma with a range to 10 ng/ml. The specificity of HLA-DR induction by IFN-gamma was demonstrated using an isotype specific monoclonal antibody as well as IFN-gamma neutralizing monoclonal and polyclonal antibodies. The effect of other cytokines on HLA-DR induction with COLO 205 cells was also investigated in this bioassay and only IFN-beta and interleukin-1 (IL-1) showed slight induction of HLA-DR. IFN-alpha had no effect at the concentration tested. Evaluation of assay parameters including reproducibility, sensitivity, simplicity, speed, cost and ability to standardize support the conclusion that this bioassay is a substantial improvement over the routinely used viral inhibition assay as a measure of IFN-gamma biological activity. The bio-ELISA technique also has potential applications for the quantitation of other cellular surface antigens induced by cytokines.

Homologous human macrophage hybridomas that produce a novel cytotoxic factor in their culture supernatants

Homologous human macrophage hybridoma cell lines were obtained by somatic cell fusion between peripheral blood monocyte-derived macrophages and a subclone of the myelomonocytic cell line, U937-F9. The hybridoma cell lines grown in vitro for more than a year were confirmed by manifestations of phagocytosis, adherence, nonspecific esterase, acid phosphatase, chromosome numbers and other cell surface antigens. Cell surface antigens on hybridomas were detected by flow cytometry analysis with monoclonal antibodies. With interclonal differences, a typical phenotype of hybridoma cells was CDw14+, OKM5+, Mac-1+ (equivalent to OKM1 and Mol), OKT9+, HLA-DR- and CD20+. After stimulation with lipopolysaccharide and calcium ionophore A23187, culture supernatants of clones c18A and c29A showed cytotoxic activity against human melanoma A375 Met-Mix and other cell lines which were resistant to the tumor necrosis factor, lymphotoxin and interleukin 1. This cytotoxic factor was found to be distinct from the tumor necrosis factor, lymphotoxin and interleukin 1 using the anti-tumor necrosis factor, anti-lymphotoxin and anti-interleukin 1 antisera.