Immunochemical analysis of the released Leu-2 (T8) molecule

Low on-treatment levels of serum soluble CD8 (sCD8) predict better outcomes in advanced non-small cell lung cancer patients treated with atezolizumab

BACKGROUND

Immunotherapy has changed the paradigm of treating non-small cell lung cancer (NSCLC). But, selecting patients who will achieve long-term benefits from treatment remains unsatisfactory. Here, we investigated the possible use of the soluble form of CD8 antigen (sCD8) in predicting durable disease control after PD-1/PD-L1 blockade. CD8 is a marker of the cytotoxic T lymphocytes. Its soluble form (sCD8) is secreted under activation of the immune system but also has immunosuppressive properties. The data about serum sCD8 in patients dosed with anti-PD-1/PD-L1 drugs are lacking.

METHODS AND RESULTS

We included 42 NSCLC patients and collected samples at baseline and for the first 3 months of atezolizumab immunotherapy. The serum sCD8 concentrations were measured with the ELISA kit and correlated with treatment outcomes. Patients with durable (≥ 12 months) disease control presented lower serum sCD8 than those without long-term benefits. The sCD8 levels measured at the end of cycle 2 (sCD8.2) were the earliest time point that successfully differentiated patients (3.76 vs. 9.68 ng/mL, respectively, p < 0.001). Individuals with low sCD8.2 (≤ 4.09 ng/mL) presented longer progression-free survival (HR = 0.061, p < 0.001) and overall survival (HR = 0.104, p < 0.05) compared to individuals with high sCD8.2 (median values unreached vs. 4.4 months and 14.4 months for PFS and OS, respectively).

CONCLUSIONS

Serum sCD8 could be an early biomarker of durable disease control after anti-PD-L1 treatment. Higher sCD8 in patients with worse outcomes could suggest the inhibitory effect of sCD8 on cytotoxic T-cells activation.

SheddomeDB: the ectodomain shedding database for membrane-bound shed markers

BACKGROUND

A number of membrane-anchored proteins are known to be released from cell surface via ectodomain shedding. The cleavage and release of membrane proteins has been shown to modulate various cellular processes and disease pathologies. Numerous studies revealed that cell membrane molecules of diverse functional groups are subjected to proteolytic cleavage, and the released soluble form of proteins may modulate various signaling processes. Therefore, in addition to the secreted protein markers that undergo secretion through the secretory pathway, the shed membrane proteins may comprise an additional resource of noninvasive and accessible biomarkers. In this context, identifying the membrane-bound proteins that will be shed has become important in the discovery of clinically noninvasive biomarkers. Nevertheless, a data repository for biological and clinical researchers to review the shedding information, which is experimentally validated, for membrane-bound protein shed markers is still lacking.

RESULTS

In this study, the database SheddomeDB was developed to integrate publicly available data of the shed membrane proteins. A comprehensive literature survey was performed to collect the membrane proteins that were verified to be cleaved or released in the supernatant by immunological-based validation experiments. From 436 studies on shedding, 401 validated shed membrane proteins were included, among which 199 shed membrane proteins have not been annotated or validated yet by existing cleavage databases. SheddomeDB attempted to provide a comprehensive shedding report, including the regulation of shedding machinery and the related function or diseases involved in the shedding events. In addition, our published tool ShedP was embedded into SheddomeDB to support researchers for predicting the shedding event on unknown or unrecorded membrane proteins.

CONCLUSIONS

To the best of our knowledge, SheddomeDB is the first database for the identification of experimentally validated shed membrane proteins and currently may provide the most number of membrane proteins for reviewing the shedding information. The database included membrane-bound shed markers associated with numerous cellular processes and diseases, and some of these markers are potential novel markers because they are not annotated or validated yet in other databases. SheddomeDB may provide a useful resource for discovering membrane-bound shed markers. The interactive web of SheddomeDB is publicly available at http://bal.ym.edu.tw/SheddomeDB/ .

Human mesenchymal stem cells shift CD8+ T cells towards a suppressive phenotype by inducing tolerogenic monocytes

The mechanisms underlying the immunomodulatory effects of mesenchymal stem cells (MSCs) have been investigated under extreme conditions of strong T cell activation, which induces the rapid death of activated lymphocytes. The objective of this study was to investigate these mechanisms in the absence of additional polyclonal activation. In co-cultures of peripheral mononuclear blood cells with human MSCs (hereafter referred to as hMSCs), we observed a striking decrease in the level of CD8 expression on CD8+ cells, together with decreased expression of CD28 and CD44, and impaired production of IFN-gamma and Granzyme B. This effect was specific to hMSCs, because it was not observed with several other cell lines. Downregulation of CD8 expression required CD14+ monocytes to be in direct contact with the CD8+ cells, whereas the effects of hMSCs on the CD14+ cells were essentially mediated by soluble factors. The CD14+ monocytes exhibited a tolerogenic pattern when co-cultured with hMSCs, with a clear decrease in CD80 and CD86 co-stimulatory molecules, and an increase in the inhibitory receptors ILT-3 and ILT-4. CD8+ cells that were preconditioned by MSCs had similar effects on monocytes and were able to inhibit lymphocyte proliferation. Injection of hMSCs in humanized NSG mice showed similar trends, in particular decreased levels of CD44 and CD28 in human immune cells. Our study demonstrates a new immunomodulation mechanism of action of hMSCs through the modulation of CD8+ cells towards a non-cytotoxic and/or suppressive phenotype. This mechanism of action has to be taken into account in clinical trials, where it should be beneficial in grafts and autoimmune diseases, but potentially detrimental in malignant diseases.

Soluble CD-4 and CD-8 as markers of immunological activation in renal transplant recipients

BACKGROUND

T lymphocytes are activated following kidney transplantation in cases of acute graft rejection and viral infections. In plasma, elevated levels of T-cell markers can be measured in soluble form. The reason for this shedding is still not entirely understood.

METHODS

Plasma concentrations of soluble CD-4 and CD-8 (sCD-4, sCD-8) were determined in 78 patients following kidney transplantation by commercially available enzyme-linked immunosorbent assay (ELISA) test kits.

RESULTS

The concentrations of both soluble T-cell markers increased significantly in the course of acute allograft rejections and cytomegalovirus (CMV) infections. Frequently, the parameters increased shortly before clinical diagnosis and decreased under successful therapy. Additionally, sCD-8 showed significant higher plasma concentrations in cases of CMV infection as compared with acute allograft rejections. Accordingly, the sCD-4/sCD-8 ratio increased in cases of acute allograft rejection and decreased during CMV infections. Cyclosporin A nephrotoxicity caused no significant changes in the sCD-4 and sCD-8 levels in plasma.

CONCLUSION

The present study demonstrates that sCD-4 and sCD-8 are markers of immunological activation and may enable a further differentiation of T-cell activation if serial measurements are performed. However, further prospective investigations are necessary to elucidate the diagnostic potential of sCD-4 and sCD-8 for monitoring acute rejection and viral infection in kidney graft recipients.

Soluble CD8 stabilizes the HLA class I molecule by promoting beta2M exchange: analysis in real-time

Human soluble CD8 (sCD8) is secreted by activated CD8+/- cytotoxic T lymphocytes (CTLs). The immunological role of sCD8 is poorly defined, however. We have studied the influence of sCD8 on HLA class I interactions by real-time analysis. Using an optical biosensor we demonstrated that the binding of sCD8 to HLA-A2 promotes exchange of beta2-microglobulin (beta2m) in order to stabilize the complex. Kinetic analysis showed that sCD8 significantly increased the affinity (K(A)) of HLA-A2 for immobilized human beta2m; from 1.14 +/- 0.04 x 10(9) M(-1) in its absence, to 2.18 +/- 0.21 x 10(9) M(-1) following preincubation with sCD8. This suggests that the sCD8:HLA class I complex is unlikely to be degraded at the cell surface. Even in the presence of exogenous peptide (HLA-A2 specific or nonspecific), sCD8 has a stabilizing influence on the HLA class I molecule. These findings point to an immunosuppressive role for sCD8, because the binding of sCD8 to HLA class I would block the binding site for CTL-bound CD8 and, therefore, interfere with T cell activation and proliferation. This may have particular significance in pathological situations where elevated levels of sCD8 are found in extracellular fluids, and sCD8 may provide an alternative approach for immunosuppressive therapy.

Changes in immune activation markers during pregnancy and postpartum

Changes in CD4 + cell levels and other immune parameters have been reported to occur during pregnancy but the timing of these alterations and their relationship to changes in immune function have not been well characterized. In addition, the influence of sociodemographic, obstetric, and other covariates on these relationships is largely unknown. We measured three immune activation markers, soluble interleukin-2 receptor (sIL-2Ralpha), soluble CD8 antigen (sCD8), and neopterin during pregnancy and postpartum in 170 HIV-1-seronegative women enrolled in the Mothers and Infants Cohort Study. Ante-partum and postpartum changes in these markers were examined using multivariable longitudinal random effects models. Neopterin levels began to rise well before delivery and were in decline by 2 months postpartum. sIL-2Ralpha and sCD8 levels increased at or near delivery and peaked by 2 months postpartum. After adjustment for other variables, the peak in sIL-2Ralpha was greater among women with pre-term than full-term deliveries (P = 0.05). All three markers were higher in whites than non-whites and in 'hard' drug users than non-users (P < or = 0.001 for each). After adjustment for these and other variables, hepatitis C virus (HCV) seropositivity was associated with higher levels of sCD8 and neopterin (P < or = 0.001 for each) but not sIL-2Ralpha (P = 0.27). These longitudinal data indicate that a state of broad immune activation develops at or near delivery. A number of maternal variables appear to influence the magnitude of these changes.

Membrane protein secretases

A diverse range of membrane proteins of Type 1 or Type II topology also occur as a circulating, soluble form. These soluble forms are often derived from the membrane form by proteolysis by a group of enzymes referred to collectively as 'secretases' or 'sheddases'. The cleavage generally occurs close to the extracellular face of the membrane, releasing physiologically active protein. This secretion process also provides a mechanism for down-regulating the protein at the cell surface. Examples of such post-translational proteolysis are seen in the Alzheimer's amyloid precursor protein, the vasoregulatory enzyme angiotensin converting enzyme, transforming growth factor-alpha, the tumour necrosis factor ligand and receptor superfamilies, certain cytokine receptors, and others. Since the proteins concerned are involved in pathophysiological processes such as neurodegeneration, apoptosis, oncogenesis and inflammation, the secretases could provide novel therapeutic targets. Recent characterization of these individual secretases has revealed common features, particularly sensitivity to certain metalloprotease inhibitors and upregulation of activity by phorbol esters. It is therefore likely that a closely related family of metallosecretases controls the surface expression of multiple integral membrane proteins. Current knowledge of the various secretases are compared in this Review, and strategies for cell-free assays of such proteases are outlined as a prelude to their ultimate purification and cloning.

Soluble CD4 and CD8 in serum from patients with localized scleroderma

Localized scleroderma has been shown to be accompanied by various immunologic abnormalities. To obtain functional information on activated CD4+ or CD8+ T cells, we studied the levels of soluble CD4 (sCD4) and soluble CD8 (sCD8) in serum from patients with localized scleroderma. Serum samples were examined by enzyme-linked immunosorbent assay. The samples were obtained from 49 patients in the following three subgroups: 15 patients with generalized morphea, 22 with linear scleroderma, and 12 with morphea. The levels of sCD4 and sCD8 were significantly elevated in patients with generalized morphea. Furthermore, these patients showed significantly higher levels of sCD4 than those with systemic sclerosis (SSc). The frequency of positivity for IgG anti-single-stranded DNA (ssDNA) antibody was significantly higher in localized scleroderma patients with elevated sCD4 levels than in patients with normal sCD4 levels. The frequency of positivity for antinuclear antibodies, IgM antihistone antibodies, IgG anti-ssDNA antibody and rheumatoid factor, and elevated sCD23 levels were significantly higher in localized scleroderma patients with elevated sCD8 levels than in patients with normal sCD8 levels. Our findings suggest that both CD4+ and CD8+ T cells are activated in vivo in generalized morphea and that the immunologic events in generalized morphea are different from those in SSc.

Effect of ranitidine on soluble interleukin 2 receptors and CD8 molecules in surgical patients

The effect of perioperative immunomodulation with the H2-receptor antagonist ranitidine on postoperative changes in soluble interleukin (IL) 2 receptor and soluble CD8 levels was assessed in 24 patients undergoing major elective abdominal surgery. Eleven patients were randomized to receive intravenous ranitidine 100 mg twice daily for 4 days from skin incision, followed by oral ranitidine 150 mg twice daily for a further 5 days; 13 control patients received no ranitidine. Routine blood analysis, clinical data, duration of surgery, anaesthesia, antibiotic prophylaxis and perioperative blood transfusion were similar in the two groups. Serum concentrations of soluble IL-2 receptor and CD8 were measured before operation (day 0) and in the morning of postoperative days 1, 3 and 9 using commercial enzyme-linked immunosorbent assay kits. In patients treated with ranitidine, the serum level of soluble IL-2 receptor increased from day 0 to day 9 (P < 0.01); in control patients it decreased from day 0 to day 1, did not change significantly by day 3 and increased by day 9. The change from day 0 to day 1 was significantly different between the two groups (P < 0.01). Five of the 13 control patients developed postoperative infectious complications. No significant differences were shown in soluble CD8 concentration during the postoperative period. The postoperative change in soluble IL-2 receptor level may reflect lymphocyte activation status; ranitidine appears to promote activation of mainly CD4-positive lymphocytes since serum levels of CD8 were unchanged. Ranitidine may, therefore, improve immune function during major surgery.

Impaired antibody levels to tetanus toxoid and pneumococcal polysaccharides in acute leukemias

Antibody levels to the protein antigen tetanus toxoid (TTx) and the carbohydrate antigens pneumococcal capsular polysaccharides (PCP) were studied by enzyme immunoassay in 14 patients with acute lymphocytic leukemia (ALL) and 32 patients with acute non lymphocytic leukemia (ANLL) before and three weeks after initiation of chemotherapy. The antibody levels to TTx were significantly lower in ALL patients than in controls. This was associated with elevated levels of sCD8 (soluble CD8) in the serum of 12 out of the 14 ALL patients. Patients with ANLL had normal antibody levels before chemotherapy. After chemotherapy ANLL patients with septic complications had a reduced increase of antibody titers to TTx than patients without sepsis. The average antibody titers to PCP decreased in patients with sepsis, while they increased slightly in patients without sepsis. We conclude that in contrast to ANLL patients ALL patients have preexisting decreased antibody levels to thymus dependent protein antigens, while antibody levels to thymus independent carbohydrate antigens are normal in both types of leukemias.

High serum levels of soluble CD8 in insulin-dependent diabetes

In type 1 (insulin-dependent) diabetes mellitus (IDDM) CD8+ T cells represent the majority of lymphocytes which infiltrate the pancreatic islets during beta cell destruction. Soluble CD8 antigen (sCD8) has been shown to correlate with CD8 cell subset activation. In this study we measured by ELISA sCD8 levels in sera from: 33 newly diagnosed IDDM patients; 29 type 1 diabetics with duration of disease more than 1 year; 37 healthy siblings of IDDM patients; 19 healthy controls. Sera from both groups of IDDM patients and from healthy siblings exhibited soluble CD8 mean levels significantly higher than controls (P = 0.0001, P < 0.003, P < 0.03 respectively). Soluble CD8 levels above the normal range (mean +/- 2 s.d. of controls) were found in a percentage of newly diagnosed subjects (54.5%) significantly higher than in subjects with a long-standing duration of disease (6.9%, P < 0.0005) and healthy siblings (16.2%, P < 0.002). Our results suggest that the raised levels of soluble CD8 near to diabetes onset may indicate the activation of CD8+ T cells probably responsible for the autoimmune beta cell destruction.

Anti-cytokines: promising tools for diagnosis and immunotherapy

Anti-cytokines belong to a new family of biological response modifiers which interfere with the biological functions of cytokines. An imbalance between cytokines and natural anti-cytokines may represent an important factor to explain the pathogenesis of some human diseases. Indeed, dysregulation of anti-cytokine serum levels was observed in cancers and auto-immune and infectious diseases. It was sometimes associated with disease activity and in some circumstances they may help to predict clinical response to treatment. Control of disease activity in septic shock and auto-immune diseases was demonstrated after administration of anti-cytokines such as soluble TNF receptors and IL1ra inhibitors. Therefore these agents are promising tools for diagnosis and immunotherapy.

CD8 and beta 2-microglobulin-free MHC class I molecules in T cell immunoregulation

Intracellular assembly of MHC class I heavy chains with beta 2-microglobulin occurs prior to the expression of the antigen-presenting complex on the cell surface. The association of beta 2-microglobulin with newly synthesized class I heavy chains is thought to be a strict prerequisite for their transport to the cell surface. However, MHC class I molecules not associated with beta 2-microglobulin (beta 2-microglobulin-free class I heavy chains) have been detected on the surface of activated lymphoid cells. These molecules have different conformations. Therefore, their interactions with other membrane proteins and biological functions may be different from those assigned to beta 2-microglobulin-associated MHC class I molecules. The two forms of MHC class I molecules on the surface of activated cells can self-associate and also form complexes with distinct proteins. Upon interaction with the appropriate ligands these molecular complexes transduce signals regulating cell activation. The ligand for beta 2-microglobulin-free class I heavy chains appears to be soluble CD8. A model is presented describing a novel mechanism of immunoregulation mediated by both soluble and membrane-bound forms of CD8 and beta 2-microglobulin-free class I heavy chains.

Early sCD8 plasma levels during subcutaneous rIl-2 therapy in patients with renal cell carcinoma correlate with response

Plasma sIl-2R and sCD8 levels of 12 patients with renal cell carcinoma were determined before and during subcutaneous rIl-2 therapy. Patients with a complete/partial remission showed a significantly stronger initial increase of sCD8 compared to patients with stable disease or tumour progression.

Serum soluble CD4, CD8 and IL-2R levels in adult acute myeloid leukemia in remission

We have measured the serum levels of soluble CD4, CD8 and IL-2R in 43 patients with AML in complete remission (AML-CR). The sCD8 levels of AML-CR patients (443.9 +/- 224.4 u/ml) were significantly high as compared to that of the normal controls (177.1 +/- 76.3 u/ml), p < 0.01. The sIL-2R levels of AML-CR patients were 715.0 +/- 646.3 u/ml, which significantly differed when compared to 322.1 +/- 65.7 u/ml for the normal controls, p < 0.01. However, the sCD4 levels of AML-CR patients were 9.6 +/- 4.7 u/ml, which did not differ from the 8.3 +/- 2.6 u/ml of the normal controls. The AML-CR patients showed significantly increased sCD8 and sIL-2R levels at all ranges during the remission from one to 188 months. The sCD8 levels and sIL-2R levels of the AML-CR patients showed a close correlation, p < 0.01. Further, the sCD8 levels and lymphokine activated killer cell cytotoxic activity showed a close correlation, p < 0.05. The presence of the activation of anti-tumor immunity may be related to the continuance of the remission in the AML-CR patients.

Increases in soluble CD8 antigen in plasma, and CD8+ and CD8+CD38+ cells in human immunodeficiency virus type-1 infection

Increases in plasma levels of soluble CD8 (SCD8) antigen and expansion of the CD8+ CD38+ lymphocyte compartment were early immunologic alterations frequently observed prior to detection of antibodies against human immunodeficiency virus type 1 (HIV-1) and diminution of CD4+ cells in subjects at risk to develop AIDS. These increases identified in the 49 seronegative homosexual men were manifest in all 164 homosexual subjects and 45 intravenous drug users (IVDU) positive for HIV-1 antibodies (HIV-1+), 19 patients with ARC, and 29 AIDS patients. Augmentation of plasma sCD8 antigen correlated with increases in both CD8+ and CD8+ CD38+ cells in HIV-1(-) homosexual men (r = 0.35, P less than 0.013; r = 0.48, P less than 0.0005; respectively) and the 258 HIV-1+ subjects (r = 0.25, P less than 0.0003; r = 0.33, P less than 0.0001, respectively). In vitro examination of unstimulated peripheral blood lymphocytes from HIV-1+ homosexuals and IVDU confirmed the fivefold higher constitutive levels of cellular release of sCD8 antigen in these subjects compared to heterosexual controls. Inclusion of radiolabeled amino acids during the 3-day culture period in the presence or absence of phytohemagglutinin resulted in negligible levels of radioactivity associated with the sCD8 antigen indicative of a lack of de novo synthesis. Throughout clinical progression to AIDS, sCD8 antigen levels continued to escalate relative to the numbers of CD8+ cells bearing CD38+ antigen. The data confirm the interrelationship between sCD8+ antigen and CD8+ and CD8+ CD38+ cells.

High serum levels of CD8 antigen in primary biliary cirrhosis: a possible cause of suppressor cell dysfunction?

Reduced suppressor cell number and function have been described in a number of autoimmune diseases and this may contribute to pathogenesis. Suppressor cell function depends upon the interaction of the CD8 antigen expressed on suppressor cells with other limbs of the immune system. Recently, soluble membrane antigens including CD8 have been identified in serum and it is possible that the loss of such antigens from viable cells could result in functional deficit. In order to examine whether the decreased suppressor cell function reported in autoimmune type of chronic liver disease is associated with soluble serum CD8 levels, sera from 23 patients with primary biliary cirrhosis (PBC), 12 with autoimmune chronic active hepatitis (AI-CAH) and 21 healthy controls were tested using a commercially available enzyme immunoassay. The proportion of cells expressing the CD8 antigen and the intensity of its display were also determined using an immunofluorescent technique and an ELISA, respectively, for 12 PBC and 10 healthy controls. The soluble serum CD8 levels were significantly higher in PBC (mean U/ml +/- s.d., 777 +/- 331), and AI-CAH (575 +/- 291) than controls (322 +/- 115) (P less than 0.001 and P = 0.004, respectively). While the intensity of CD8 antigen expression on suppressor/cytotoxic populations was not significantly different in PBC (347 +/- 125 per 10(4) cells) compared with controls (441 +/- 206), the mean proportion of CD8 positive cells was significantly less in PBC (14.1 +/- 6.8%) than controls (20 +/- 4.7%) (P less than 0.05). These data suggest that the apparent reduction in suppressor cell number found for patients with PBC and AI-CAH may be a consequence of the shedding or secretion of CD8 antigen from cell membrane of CD8 positive lymphocyte. It is also possible that the loss of this antigen is responsible for the reduced suppressor cell function seen in these conditions.

The clinical significance of serum CD8 antigen levels in adult patients with Hodgkin's disease

Increased suppressor T-cell activity has been observed in patients with Hodgkin's disease. In order to evaluate the clinical significance of soluble CD8 antigen (sCD8), which is released from CD8+ suppressor/cytotoxic T-lymphocytes, we determined sCD8 levels in the sera of 82 consecutive patients with newly diagnosed untreated Hodgkin's lymphoma who were entered into prospective trials of the German Hodgkin's Disease Study Group. sCD8 levels were significantly higher (p less than 0.01) in stage IV (781 U/ml, n = 19) than in stages I-IIIB (443 U/ml; n = 63). Patients with B-symptoms (n = 36) had slightly higher levels (611 U/ml) than patients without (n = 46) systemic symptoms (447 U/ml; p = 0.08). In 77 patients evaluable for response, the complete remission (CR) rate of patients with sCD8 less than 750 U/ml was higher (54/60 or 90%) than that of patients with sCD8 greater than 750 U/ml 11/17 or 65%; p = 0.01). The time to treatment failure was significantly longer in patients with sCD8 less than 750 U/ml (p = 0.008), even among the group with stages IIIB/IV only (p = 0.04). Our data suggest that the pretreatment levels of sCD8 in adult patients with Hodgkin's lymphoma have prognostic relevance, and that they should be determined especially in patients with advanced disease. Increased understanding of the role of sCD8 may shed light on the pathogenesis of Hodgkin's disease.

Decrease in soluble CD8 antigen levels in splenectomized patients as an index for reduced suppressor/cytotoxic cell activity

To investigate the effect of splenectomy on lymphocyte subpopulations we monitored changes in serum concentrations of soluble suppressor/cytotoxic (sCD8) and soluble helper/inducer (sCD4) antigen in 11 splenectomized patients. Indications for splenectomy were hereditary spherocytosis in 2, idiopathic thrombocytopenic purpura in 2, gastric carcinoma in 4, Hodgkin's disease in 2 and pancreatitis in 1 patient. Lymphocyte subpopulations were also analyzed by means of conventional immunophenotyping with monoclonal antibodies to CD4 and CD8. We consistently found an early postoperative drop of sCD8 and sCD4 levels within the first week after splenectomy, paralleling changes in the percentages of CD4+ and CD8+ lymphocytes. While alterations of lymphocyte subsets in the peripheral blood were completely reversible and sCD4 levels returned to preoperative values, sCD8 concentrations remained suppressed even 3 months after splenectomy. SCD8 levels at the nadir and those 3 months after splenectomy were significantly lower than preoperative values (P = 0.003, P = 0.149 respectively). Since sCD8 levels reflect suppressor/cytotoxic cell activity, we suggest that suppressor cell activity is reduced in splenectomized patients.

Monoclonal antibody against bone marrow stromal cells. Its production and characterization

Bone marrow stromal cells play an essential role in the proliferation and differentiation of hematopoietic stem cells (1, 2). As a means of analyzing of the bone marrow microenvironment immunohistochemically, we attempted to produce a rat monoclonal antibody against the murine preadipocyte line H-1 derived from long-term bone marrow culture (LTBMC) of C57BL/6 mice (3, 4). A newly established monoclonal antibody, designated R4-A9, was obtained from a hybridoma prepared by fusion of Y.B2/3.0Ag20(YO) rat myeloma cells with spleen cells of LEW rats immunized with H-1 cells. The immunofluorescence of live H-1 cells showed that the antigen reacting with this antibody was strongly expressed on the cell surface. The specificity of R4-A9 was assessed immunohistochemically on frozen sections of various tissues from normal adult mice. R4-A9 demonstrated specificity for hematopoietic stroma in bone marrow and spleen. No staining was observed in thymus, lymph nodes or other tissues examined, with the exception of Leydig cells in the testis and the endothelium of small arteries in several organs. Detailed immunohistochemical observations at both the light microscopy and electron microscopy level showed that R4-A9 selectively reacted with the sinusoidal endothelium, perisinusoidal adventitial cells (5) (adventitial reticular cells (6] and intersinusoidal reticular cells (5) and the reticular cells of the splenic red pulp. These findings indicate that reticular cells and the endothelium of the bone marrow possess the common cell surface molecules recognized by R4-A9. SDS-PAGE analysis showed that R4-A9-immunoprecipitated proteins had a molecular mass of 100 kDa under reducing conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Cyclosporine A and prednisolone inhibit lectin- and alloantigen-induced release of sCD8: correlation with proliferative responses

It has been shown previously that there is a strong correlation between the in vitro release of soluble CD8 glycoprotein (sCD8) and CD8+ T lymphocyte activation. In the present study, the lectin stimulation of peripheral blood mononuclear cells (PBMC) induced a dose-dependent release of sCD8 which correlated with the magnitude of CD8 lymphocyte activation as measured by the expression of the interleukin 2 (IL-2) receptor and HLA-DR antigen and of the T cell proliferative responses. Both the proliferative responses and the release of sCD8 were inhibited by cyclosporine A (CyA) and prednisolone (PRED) in a concentration-dependent manner. When the immunosuppressants were present for only 60 min before the initiation of the cultures, an inhibitory effect was also seen, but this was maximal only when the agents were added at the initiation of the culture period; when the addition of CyA or PRED was delayed for either 24 or 48 hr after the initiation of the culture, the degree of inhibition of the proliferative response was greatly reduced. However, there was a significant inhibition of sCD8 release by CyA even when it was added 48 hr after the culture initiation. The addition of recombinant IL-2 did not affect the lectin-induced sCD8 release. The inhibition of the lectin-induced proliferative response and sCD8 release by PRED, but not that by CyA, was reversed by the recombinant IL-2. Alloantigen stimulation also induced sCD8 release and this release was inhibited both by CyA and by PRED. These data, together with the known effects of CyA on differentiation, clonal amplification, and activation of CD8 T lymphocytes, suggest that in vitro sCD8 release occurs during the early stages of activation of CD8+ cytotoxic T cells.

An angiogenin-binding protein from endothelial cells

A 42-kDa bovine protein that binds bovine angiogenin [angiogenin binding protein (AngBP)] has been identified as a dissociable cell-surface component of calf pulmonary artery endothelial cells and a transformed bovine endothelial cell line, GM7373. Binding of 125I-labeled bovine angiogenin (125I-Ang) to AngBP occurs with an apparent Kd approximately 5 x 10(-10) M and is specific, saturable, and inhibited by excess unlabeled angiogenin. 125I-Ang can be crosslinked efficiently to AngBP by a water-soluble carbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)carbo-diimide. Bovine ribonuclease A competes with the binding of 125I-Ang to AngBP, but lysozyme does not. Direct binding to AngBP of 125I-labeled bovine ribonuclease A is, however, much weaker than that of 125I-Ang. Two enzymatically active derivatives of angiogenin cleaved at residues 60-61 and 67-68, respectively, fail to induce angiogenesis and also bind to AngBP only weakly. AngBP has been isolated by treatment of cells with heparan sulfate, affinity chromatography on angiogenin-Sepharose of the material dissociated from the cell surface, and gel filtration HPLC. The results suggest that AngBP has the characteristics of a receptor that may likely function in angiogenesis.

Elevated levels of soluble CD8 molecule in patients with lymphatic filariasis

The serum levels of soluble forms of suppressor/cytotoxic cells (sCD8) and interleukin-2 receptor (sCD25) were analyzed in 67 patients with lymphatic filariasis and 28 normal controls. Our results show that patients with lymphatic filariasis have significantly higher levels of sCD8 (p less than 0.05) than the control groups, whereas no such difference was observed for sCD25. Within the patient group, however, those in the chronic lymphatic obstruction (CP) had significantly higher levels of both sCD8 (491 +/- 52 U/ml, p less than 0.001) and sCD25 (293 +/- 36 U/ml; p less than 0.02) than those with asymptomatic microfilaremia (sCD8 344 +/- 32 U/ml; sCD25 190 +/- 10 U/ml, respectively). No statistically significant correlation was observed between the serological levels of sCD8 and the percentage of CD8 on peripheral blood T lymphocytes in any of the patient groups. Evaluation of the activation state of B lymphocyte did not reveal any difference in the cellular expression of B7, or serum levels of soluble CD23 in any of the groups studied. Thus the selective increase of sCD8 in patients with filariasis suggests a possible pathogenic role of the cells involved in the release of this molecule.

Shedding of tumor necrosis factor receptors by activated human neutrophils

The capacity of human neutrophils (PMN) to bind tumor necrosis factor (TNF) was rapidly lost when the cells were incubated in suspension with agents that can stimulate their migratory and secretory responses. Both physiological (poly)peptides (FMLP, C5a, CSF-GM) and pharmacologic agonists (PMN, calcium ionophore A23187) induced the loss of TNF receptors (TNF-R) from the cell surface. Half-maximal loss in TNF-R ensued after only approximately 2 min with 10(-7) M FMLP at 37 degrees C, and required only 10(-9) M FMLP during a 30-min exposure. However, there were no such changes even with prolonged exposure of PMN to FMLP at 4 degrees or 16 degrees C. Scatchard analysis revealed loss of TNF-binding sites without change in their affinity (Kd approximately 0.4 nM) as measured at incompletely modulating concentrations of FMLP, C5a, PMA, or A23187. The binding of anti-TNF-R mAbs to PMN decreased in parallel, providing independent evidence for the loss of TNF-R from the cell surface. At the same time, soluble TNF-R appeared in the medium of stimulated PMN. This inference was based on the PMN- and FMLP-dependent generation of a nonsedimentable activity that could inhibit the binding of TNF to fresh human PMN or to mouse macrophages, and the ability of mAbs specific for human TNF-R to abolish inhibition by PMN-conditioned medium of binding of TNF to mouse macrophages. Soluble TNF-R activity was associated with a protein of Mr approximately 28,000 by ligand blot analysis of cell-free supernatants of FMLP-treated PMN. Thus, some portion of the FMLP-induced loss of TNF-R from human PMN is due to shedding of TNF-R. Shedding was unaffected by inhibitors of serine and thiol proteases and could not be induced with phosphatidylinositol-specific phospholipase C. Loss of TNF-R from PMN first stimulated by other agents may decrease their responsiveness to TNF. TNF-R shed by PMN may be one source of the TNF-binding proteins found in body fluids, and may blunt the actions of the cytokine on other cells.

Soluble interleukin-2 receptor and soluble CD8 in serum and cerebrospinal fluid during human immunodeficiency virus-associated neurologic disease

We have measured levels of soluble interleukin-2 receptor (sIL-2R) and soluble CD8 (sCD8) in serum and cerebrospinal fluid (CSF) of 127 human immunodeficiency virus (HIV)-seropositive and 51 HIV-seronegative individuals. Serum levels of sIL-2R and sCD8 were higher in HIV+ than in HIV- individuals. HIV+ individuals were grouped by neurological status: asymptomatic, abnormal on neuropsychological screening, HIV-related meningitis, inflammatory demyelinating polyneuropathy, opportunistic central nervous system (CNS) infections and HIV-related dementia, myelopathy or sensory neuropathy. Serum levels of sIL-2R and sCD8 were higher in all HIV+ categories compared to HIV- individuals. Patients with HIV-related meningitis had higher levels of sIL-2R and sCD8 than asymptomatic HIV+ individuals, and inflammatory polyneuropathy patients had higher levels of sCD8. CSF levels of sCD8 were higher in all categories of HIV+ than in HIV- individuals. Patients with HIV-related meningitis, inflammatory neuropathy and opportunistic infections had higher levels than asymptomatic individuals. Examination of the time course showed that serum and CSF levels of sIL-2R and sCD8 increased to very high levels during acute HIV infections. Serum levels then declined over several months to relatively stable elevated levels. By 1-2 years after HIV infection sIL-2R was relatively low in CSF, while sCD8 remained elevated with a gradual decrease over the subsequent years of follow-up.

Soluble CD8 in patients with rheumatic diseases

An ELISA was used to measure soluble CD8 (sCD8) in the sera and synovial fluids (SF) of patients with rheumatic diseases. Patients with rheumatoid arthritis (RA) had raised levels of sCD8 both in their sera and in their SF compared with patients with osteoarthritis and age-matched healthy controls. In individual RA patients, serial serum sCD8 levels initially fell and then rose preceding clinical improvement. In four patients where serum sCD8 levels rose and clinical improvement occurred, subsequent spontaneous decreases of serum sCD8 level preceded increased clinical disease activity by up to 2 weeks. In general, RA SF mononuclear cells (SFMNC) spontaneously produced high levels of sCD8. In contrast, autologous peripheral blood MNC only produced comparable levels after mitogenic stimulation. Incubation of SFMNC with increasing concentrations of human recombinant tumour necrosis factor alpha resulted in a dose-dependent potentiation of sCD8 release into the supernatant. There was an inverse relationship between the ability of SFMNC to release sCD8 and soluble interleukin-2 receptor, indicating that the CD8+ T cell population may play an important immunoregulatory role in RA.

Analysis of a soluble mutant des-methionine interleukin-2 receptor alpha chain (Tac protein) produced by transfected mammalian cells

By using recombinant DNA technology the cytoplasmic and trans-membrane domain of the human interleukin-2 receptor alpha chain (IL-2R alpha, Tac) and of a mutant protein lacking methionine-residues 18, 25, 44, 88, 92, 126, 149, 167, 205, and 209 (des-Met IL-2R alpha) encoded by a chemically and enzymatically synthesized gene, were deleted. This leads to secretory expression of soluble wild-type and des-Met mutant Tac protein of 42-45 kDa after transfection of BHK-21 cells. Transfectants secreted up to 1.6 micrograms soluble wild-type IL-2R alpha protein/10(6) cells in 24 h into the culture medium. LTK- cell lines, expressing a large number of wild-type and des-Met mutant low-affinity IL-2R alpha of 50-55 kDa on their surface, shed a truncated form of the Tac protein of about 40 kDa into the culture medium. In contrast to wild-type IL-2R alpha, shedding of mutant Tac protein is strongly reduced. This phenomenon might be the result of higher protein stability of the mutant receptor which may also explain the about 10 times higher surface expression of des-Met IL-2R alpha in LTK- cells. There are no significant differences in the biosynthesis and post-translational modification of mutant or wild-type Tac proteins either in transfected LTK- or BHK-21 cells as analysed by pulse/chase labeling experiments.

Elevated soluble CD8 in the synovial fluid from patients with rheumatoid arthritis

Suppressor/cytotoxic T cells express the surface marker CD8, which can be measured in a soluble form in culture supernatants of activated human lymphocytes. Using a sandwich immunoassay, we assessed the levels of soluble CD8 (sCD8) in serum from patients with rheumatoid arthritis (RA; n = 82), patients with degenerative joint disease (DJD; n = 40), and healthy controls. There were no differences in serum sCD8 levels among these groups. In contrast, the levels of soluble CD8 in the synovial fluid (SF) from patients with RA (n = 53) were significantly increased compared with the levels in 23 samples from patients with DJD (821 +/- 110 U/ml versus 213 +/- 13 U/ml, p less than 0.001). Synovial fluid sCD8 levels in the RA group were strikingly elevated, to a maximum value of 5,026 U/ml. In the majority of RA SF specimens (39 of 53), the values were significantly higher in the SF than the serum. Although the RA group had higher values of sCD8, such values were not significantly correlated with measured laboratory or clinical parameters. Current clinical and laboratory methods of evaluating patients may not be adequate in dealing with the complexity and heterogeneity of RA. Soluble CD8 values may be useful in further grouping patients with this disease.

Immune activation in measles

Measles is associated with alterations in immune regulation that sometimes lead to secondary infections or autoimmune encephalomyelitis. Simultaneously, an effective measles virus-specific immune response develops. To relate immune activation to measles and its complications, we studied the spontaneous proliferation of blood mononuclear cells and circulating levels of soluble interleukin-2 receptor and CD8 T-cell antigens in 126 patients with complicated or uncomplicated measles at various stages of the disease. Spontaneous proliferation of mononuclear cells, which was present through the first week of the rash, was greater in cells from patients with measles (8787 +/- 1403 cpm) than in those from healthy children (1529 +/- 237 cpm, P less than 0.0001). Levels of soluble interleukin-2 receptor (3385 +/- 195 units per milliliter) and CD8 (4145 +/- 437 units per milliliter) were higher in patients with measles than in those with other infectious diseases (2377 +/- 440, P = 0.003; 2399 +/- 771, P = 0.0374) or in healthy children (865 +/- 138, P less than 0.0001; 1026 +/- 169, P less than 0.0001). Levels of soluble interleukin-2 receptor were elevated before the onset of the rash and remained elevated for several weeks. In contrast, levels of soluble CD8 increased only when the rash appeared, and subsided quickly. Spontaneous proliferation of mononuclear cells and levels of soluble CD8 were similar in patients with uncomplicated disease, pneumonia, or encephalomyelitis, but soluble interleukin-2 receptor levels were lower in patients with encephalomyelitis (2312 +/- 314 vs. 3455 +/- 247 units per milliliter in uncomplicated measles; P = 0.01). In patients with encephalomyelitis, cerebrospinal fluid levels of soluble CD8 (686 +/- 350 units per milliliter), but not interleukin-2 receptor (9 +/- 8.3 units per milliliter), were increased. We conclude that the proliferative phase of the immune response, as measured by the release of soluble interleukin-2 receptor, begins before the rash appears, continues for several weeks in those without complications, but does not occur within the nervous system. In contrast, the effector phase of the immune response, as measured by the release of soluble CD8, coincides with the appearance and disappearance of the rash and occurs within the nervous system during encephalomyelitis.

Membrane anchoring and spontaneous release of CD16 (FcR III) by natural killer cells and granulocytes

CD16 is an IgG Fc receptor that is predominantly expressed on human natural killer (NK) cells and granulocytes. The CD16 antigen expressed on neutrophils is a 50 to 70-kDa glycoprotein attached to the plasma membrane by a phosphatidylinositol-glycan linkage that is susceptible to cleavage by phosphatidylinositol-specific phospholipase C (PIPLC). By contrast, treatment of NK cells with PIPLC did not cleave CD16 from the cell surface. Biochemical analysis of the deglycosylated CD16 revealed a substantial difference in the core polypeptides expressed by NK cells and granulocytes. Culture of radiolabeled NK cells resulted in the spontaneous release of a CD16 molecule, smaller than the membrane form of CD16. These findings demonstrate that structural differences exist in the CD16 antigens expressed on NK cells and granulocytes that may potentially influence their functional activities.

Elevated soluble CD8 levels in sera of human immunodeficiency virus-infected populations

Soluble CD8 levels in sera were quantitated in asymptomatic intravenous drug abusers, homosexuals, and patients with lymphadenopathy or acquired immunodeficiency syndrome. Soluble CD8 levels were elevated in human immunodeficiency virus-seronegative intravenous drug abusers and homosexuals, probably reflecting infections like cytomegalovirus. The sera of human immunodeficiency virus-seropositive groups of patients with human immunodeficiency virus infection also had elevated levels of soluble CD8, reflecting infections like cytomegalovirus and human immunodeficiency virus infection.

A secreted form of the human lymphocyte cell surface molecule CD8 arises from alternative splicing

The human lymphocyte differentiation antigen CD8 is encoded by a single gene that gives rise to a 33- to 34-kDa glycoprotein expressed on the cell surface as a dimer and in higher molecular mass forms. We demonstrate that the mRNA is alternatively spliced so that an exon encoding a transmembrane domain is deleted. This gives rise to a 30-kDa molecule that is secreted and exists primarily as a monomer. mRNA corresponding to both forms is present in peripheral blood lymphocytes, Con A-activated peripheral blood lymphocytes, and three CD8+ T-cell lines, with the membrane form being the major species. However, differences in the ratio of mRNA for membrane CD8 and secreted CD8 exist. In addition, the splicing pattern we observe differs from the pattern found for the mouse CD8 gene. This mRNA is also alternatively spliced, but an exon encoding a cytoplasmic region is deleted, giving rise to a cell surface molecule that differs in its cytoplasmic tail from the protein encoded by the longer mRNA. Neither protein is secreted. This is one of the first examples of a different splicing pattern between two homologous mouse and human genes giving rise to very different proteins. This represents one mechanism of generating diversity during speciation.

Immunocytological and immunochemical analysis on the common acute lymphoblastic leukemia antigen (CALLA): evidence that CALLA on ALL cells and granulocytes are structurally related

The common acute lymphoblastic leukemia antigen(CALLA) on acute lymphoblastic leukemia(ALL) cells and granulocytes were compared by newly developed and other anti-CALLA monoclonal antibodies(anti-CALLA). New anti-CALLA(IF-3 through IF-7) were effectively selected by immunostaining on kidney sections. By competitive binding three antigenic determinants were separated on ALL cells by IF and other anti-CALLA. All three determinants existed on granulocytes although the reactivity of each anti-CALLA was variable. Such a variability was partly due to the heterogeneous terminal sialic acid compositions. Although CALLA from granulocytes and ALL cells differed in molecular weight they showed identical peptide mapping patterns. These results strongly suggest that CALLA on ALL cells and granulocytes are structurally related although they are different in posttransulational modification.

Gene transfer of the Ly-3 chain gene of the mouse CD8 molecular complex: co-transfer with the Ly-2 polypeptide gene results in detectable cell surface expression of the Ly-3 antigenic determinants

The CD8 molecule is a glycoprotein expressed on a subset of mature T lymphocytes. It has been postulated to be a receptor for class I major histocompatibility complex molecules. In the mouse, CD8 is a heterodimer composed of Ly-2 and Ly-3 chains. We have isolated and analyzed cDNA and cosmid clones corresponding to the Ly-3 subunit. One of the isolated, cosmid clones was subsequently transfected, alone or in combination with the Ly-2 gene, into mouse Ltk- cells. Analysis of the Ly-2,3 molecules expressed at the surface of the double transfectants indicated that they are serologically and biochemically indistinguishable from their normal counterparts expressed on lymphoid cells. Ltk- cells transfected with the Ly-2 gene alone were shown to react with a subset of anti-CD8 monoclonal antibodies whereas Ly-3 transfectants did not stain with any of the anti-Ly-3 antibodies employed in this study. Since at least one of these antibodies (53-5.8) has been previously shown to recognize an epitope which is retained on the Ly-3 subunit after dissociation of the heterodimeric Ly-2,3 complex, these observations suggest that the expression of the Ly-2 polypeptide is required to permit the detectable cell surface expression of the antigenic determinants carried by the Ly-3 subunit.

Coordinated action of IgE and a B-cell-stimulatory factor on the CD23 receptor molecule up-regulates B-lymphocyte growth

The CD23 (BLAST-2) antigen, recently identified as the low-affinity IgE receptor of B lymphocytes, has also been implicated as the focus for growth-promoting signals delivered to activated B cells by a low molecular weight B-cell growth factor (BCGF). Here we show that IgE and BCGF can coordinate B-lymphocyte growth through their opposing effects on the CD23 molecule. While the activation of purified quiescent B cells with phorbol 12-myristate 13-acetate led to the induction of 45-kDa CD23 at the surface membrane, the inclusion of IgE increased CD23 expression by a factor of approximately equal to 5. The addition of BCGF resulted in the rapid release of a 35-kDa form of CD23 from the cell surface. This shed molecule is associated with autocrine growth factor activity. Substantially more of this material was generated by BCGF acting on cells that had been stimulated in the presence of IgE. The combined effects of IgE and BCGF on DNA synthesis in activated B cells were more than additive. IgE similarly augmented the stimulatory capacity of a CD23 antibody that mimics the biological actions of BCGF. Binding of the anti-receptor antibody to its 45-kDa target at the B-cell surface also prompted the release of the 35-kDa soluble species. These results demonstrate a pleiotropy in the CD23 molecule with regard to both ligand binding and the subsequent behavior of the receptor. The ability of this single receptor to orchestrate a B-lymphocyte response through a variety of ligands and its role in normal and transformed autocrine growth are discussed.

Fetal and neonatal development of human spleen: an immunohistological study

Localization and immunophenotype of lymphocyte subsets in fetal human spleens were studied by employing a panel of monoclonal antibodies (McAb) in an immunoperoxidase staining procedure on frozen tissue sections. Spleens varied from 15 weeks of gestational age (gestational weeks, gw) to newborn. The white pulp consisted of intermediate-sized lymphocytes; no separate compartments could be discerned. Germinal centre development was not observed. Dendritic cells stained for B2, HB5, aC3bR, anti-DRC and OKIa, but in most cases not for immunoglobulin. Although low cellular immunity is observed in neonates, T cells showed adult phenotypes in proportions comparable to the adult situation; immature OKT6(+) lymphocytes were rarely seen. Very few cells stained with anti-NK cell antibody Leu7. B cells all expressed B1, Leu14, aC3bR, T10 and OKIa, were strongly positive for BA1, and mostly stained very weakly for B2 and HB5. Almost all B cells expressed IgM and IgD simultaneously, and very few expressed IgG. IgA-positive cells were absent. At 15 gw a considerable number of IgM(+) B cells showed Leu1 staining, but this decreased during development. These cells may represent the normal counterpart of Leu1(+) IgM(+) cells observed in B-CLL and immunocytic and centrocytic malignant lymphomas. After 25 gw only very few Leu1(+) IgM(+) cells were seen. Altogether, the morphology and immunophenotype of white pulp B cells were different from the predominating adult B-cell subsets, at least until birth. These 'immature' splenic B cells may be precursors for adult splenic B-cell subsets. Considering the presumed role of the marginal zone in the immunity against TI-2 antigens, the absence of a marginal zone at birth may be a main factor in the defective immunity against these antigens in neonates.

A subset of OKT4+ peripheral T cells can generate colonies containing mixed progeny with OKT4+ helper and OKT8+ suppressor cells

The membrane phenotype of human T cell colony progenitors and that of their clonal progeny was studied for expression of the T4 and T8 determinants. Using clonal culture conditions, the colonies were grown in semi-solid agar medium from peripheral blood cells. Clonality was assessed using the glucose-6-phosphate-dehydrogenase isoenzyme marker. Combination of this marker with the culture of sorted cell fractions allowed us to ascribe the colony progenitors to a subset of OKT4+ lymphocytes. The progeny consisted of the mixture of single OKT4+, single OKT8+ and double OKT4+8+ cells, as determined by double staining. Double staining was performed on mass-harvested colony cells and on individual colonies expanded in liquid culture with fresh interleukin 2. Expression of the OKT8 positivity on colony cells deriving from OKT4+ progenitors required an interaction with radioresistant OKT8+ cells that were co-cultured with these progenitors. Furthermore, the functional capacities of the cell progeny were assayed on the pokeweed mitogen-driven immunoglobulin production by B cells. It was found that OKT4+ colony cells were helper whereas OKT8+ colony cells were suppressor cells. It is concluded that a subset of OKT4+ peripheral blood T lymphocytes can generate colonies containing both helper OKT4+ cells and suppressor OKT8+ cells.