Soluble donor HLA class I and beta 2m-free heavy chain in serum of lung transplant recipients: steady-state levels and increases in patients with recurrent CMV infection, acute rejection episodes, and poor outcome

Downregulation of HLA Class I Renders Inflammatory Neutrophils More Susceptible to NK Cell-Induced Apoptosis

Neutrophils are potent effector cells and contain a battery of harmful substances and degrading enzymes. A silent neutrophil death, i.e., apoptosis, is therefore of importance to avoid damage to the surrounding tissue and to enable termination of the acute inflammatory process. There is a pile of evidence supporting the role for pro-inflammatory cytokines in extending the life-span of neutrophils, but relatively few studies have been devoted to mechanisms actively driving apoptosis induction in neutrophils. We have previously demonstrated that natural killer (NK) cells can promote apoptosis in healthy neutrophils. In this study, we set out to investigate how neutrophil sensitivity to NK cell-mediated cytotoxicity is regulated under inflammatory conditions. Using in vitro-activated neutrophils and a human skin chamber model that allowed collection of in vivo-transmigrated neutrophils, we performed a comprehensive characterization of neutrophil expression of ligands to NK cell receptors. These studies revealed a dramatic downregulation of HLA class I molecules in inflammatory neutrophils, which was associated with an enhanced susceptibility to NK cell cytotoxicity. Collectively, our data shed light on the complex regulation of interactions between NK cells and neutrophils during an inflammatory response and provide further support for a role of NK cells in the resolution phase of inflammation.

Soluble HLA class I molecules exert differentiated influence on renal graft condition

The function of soluble HLA (sHLA) antigens in the process of immunoregulation and especially in graft tolerance versus rejection has not yet been established. It has been suggested that donor-derived sHLA may exert an immunotolerant influence on the graft. We sought to determine the role of sHLA class I in kidney graft survival by evaluating the influence of these molecules on allotypic lymphocytotoxic antibodies and the concentration of gamma interferon (INF-gamma). Analysis of sHLA was performed indirectly utilizing their ability to inhibit lymphocytotoxic reaction dependent on complement activation. To demonstrate the inhibitory properties of sHLA, we modified the NIH microcytotoxic test. Furthermore, we determined the concentration of INF-gamma in all sera samples for comparison with the intensity of the cytotoxic test. The comparison of the intensity of cytotoxic test inhibition with the concentration of INF-gamma revealed that high concentrations of this cytokine were associated with stronger inhibition of the cytotoxic test, thus with higher concentrations of sHLA class I molecules in recipient sera. We observed that high concentrations of sHLA class I molecules in recipient sera significantly inhibited cytotoxic reactions, which could contribute to a protective influence of sHLA on renal grafts. On the other hand, the observed increase of INF-gamma concentration might be caused by sHLA themselves, which would produce a detrimental influence on a transplanted organ. Therefore we concluded that the role of sHLA class I molecules in renal graft condition remains ambiguous.

A novel sandwich ELISA for alpha1 domain based detection of soluble HLA-G heavy chains

The detection of soluble human leukocyte antigen G (HLA-G) has been a technically demanding task for several years now and various enzyme linked immunosorbent assay (ELISA) formats have been designed. However, no ELISA test has been described so far which is able to detect all possible kinds of soluble HLA-G (sHLA-G) molecules that might occur in bio fluids. Here we describe a new ELISA approach able to recognize soluble alpha1 domain containing heavy chains of all HLA-G isoforms. The detection limit is shown to be at about 150 pg soluble recombinant HLA-G1 heavy chain per milliliters. Detectable HLA-G fragments are shown to occur in the supernatants of different HLA-G transfected cell lines and appear to be particularly abundant in supernatant of trophoblast derived choriocarcinoma cell lines. The novel ELISA employs the well characterized HLA-G mAbs 4H84 and MEM-G1 which ensure high HLA-G specificity. A negative control ELISA format, designed against non-existing analytes, has been established to reveal non-specific signal interference.

CMV-infected allogeneic endothelial cells initiate responder and bystander donor HLA class I release via the metalloproteinase cleavage pathway

Although cytomegalovirus (CMV) interferes with major histocompatibility expression in infected cells, both host and donor soluble human leukocyte antigen class I (sHLA-I) are often released into the serum of transplant recipients during CMV infection and may contribute to anti-HLA antibody production and graft rejection. We hypothesized that CMV infection of endothelial cells (EC) induces host T cells to release interferon (IFN)-gamma, which in turn drives the metalloproteinase (MPase)-cleavage pathway of sHLA-I generation in "bystander" uninfected ECs. To test this hypothesis, cultures of peripheral blood mononuclear cells (PBMCs) and either uninfected ECs or CMV-infected ECs (EC/CMV) were established and supernatants were tested in enzyme-linked immunosorbent assay for sHLA-I. Responder PBMC became activated and released sHLA-I via the MPase pathway when stimulated with allogeneic EC/CMV; the sHLA-I release was contact dependent and cytokine independent. In transwell cultures, IFN-gamma released by PBMCs in response to EC/CMV stimulated a release of sHLA-I from uninfected allogeneic ECs across the transwell; this release was also MPase dependent. This implies that CMV infection within the transplanted allograft will not only stimulate the release of self HLA from responding PBMCs, but will also stimulate the release of donor sHLA-I from uninfected bystander ECs, both via the class I MPase-pathway.

Immunohistochemical and in situ detection of cytomegalovirus in lung autopsies of children immunocompromised by secondary interstitial pneumonia

Secondary interstitial pneumonia (SIP), a disease affecting patients immunocompromised by primary underlying diseases during their treatment in hospital, is frequently associated with cytomegalovirus (CMV) infection, a potentially treatable condition. However, in many cases, no infectious agent can be determined, and this clinical disease rapidly progresses to death. Theoretically, SIP could be caused by CMV, which may be present in such small amounts or such configuration that routine histopathological analysis or viral culture techniques cannot detect the virus. To test the hypothesis that immunohistochemistry (IH) and in situ detection by hybridization (ISH) provides more accurate results than the mere histological demonstration of CMV inclusions, these methods were applied to 37 autopsied lung sections obtained from children immunocompromised by primary underlying diseases and who died of SIP. As a result, the cases were subdivided into three groups: (1) children with SIP CMV inclusions (Diffuse alveolar damage-DAD-related) (n = 7); (2) children with SIP without classical viral inclusions (CMV-DAD-related) (n = 3); (3) children with SIP exhibiting nuclear cytopathic effect (not CMV-NSIP-related) (n = 27). In the first group, all three techniques yielded clearly positive results, whereas IH and ISH indicated that three of the children of the second group had CMV-related DAD without histological demonstration of CMV inclusions. In the third group, there were no positive CMV signals. These data indicate that DAD-related CMV infection is an important cause of SIP and of death in children immunosuppressed by primary underlying diseases, and that IH and in situ detection were more sensitive than the histological demonstration of CMV inclusions. A direct involvement of CMV in SIP exhibiting DAD is likely, but not in the non-specific interstitial pneumonia (NSIP) pattern. We conclude that all children with primary underlying diseases should be investigated for CMV SIP using sensitive IH and in situ tests in conjunction with histological routine procedures.

Detection in chick embryo of fetoproteins not recognized by the dam's immune system and of soluble alloantigens. Presumptive teratogenic and abortogenic capacity of their specific IgY

BACKGROUND

The aim of this work was to detect antigens, non-self to the dam, potentially present in chick embryo prior to organogenesis with a view to establishing the consequences of their neutralization on chick development. To this end, hens were immunized with the extract from embryos incubated for 53 h. Their eggs were either used to isolate immunoglobulins for dot and blot tests or incubated for variable lengths of time.

RESULTS

Immunoblot tests, using adsorbed primary and secondary antibodies against paternal serum, revealed the presence of at least four antigens of 32, 34, 70 and 200 kDa that can be classified as soluble alloantigens. The same antibodies against chick embryo extracts (between 53 h and 9) showed at least five aged antigens of 34, 52, 90, 200 and 250 kDa, not detected in cock serum, that can thus be considered as soluble, foreign to the immunized hens and transitory antigens. The abnormalities observed included arrested development and fetal death, as well as minor functional damage in the few chicks that were born alive. The ratio of abnormal to normal embryos was 2.85 in the experimental group and 0.43 in the control group. With regard to congenital anomalies it must be said that of the 81 eggs incubated only four chicks were born alive, and of these, only one had a healthy birth and subsequent growth. The other three showed a transitory ataxia and one of them presented adult lumbar scoliosis and asymmetric pelvis.

CONCLUSIONS

The problem of recurrent spontaneous abortions is revisited in the light of these results. Some recent data suggest that soluble alloantigens may be candidates for a new etiological entity in recurrent spontaneous abortions. They can also be the cause of some congenital anomalies. The soluble, foreign, transitory antigens may have a similar effect although there is no supportive data in the literature.

Size variants of beta-2-microglobulin-free human leucocyte antigen class I heavy chain make different contributions to its serum increase in multiple myeloma

We previously showed that serum beta-2-microglobulin (beta2m)-free human leucocyte antigen (HLA) class I heavy chain (FHC) levels were increased in MM and correlate with disease activity. The present investigation, carried out in 124 multiple myeloma patients, studied the expression of the three size variants of FHC, namely the 42 kDa intact heavy chain (A variant, AV), released through a shedding process, and the truncated FHC (tFHC) 39 kDa (BV) and 36-35 kDa (CV) released by means of membrane-type metalloprotease activity. The increase in FHC correlated with a high expression percentage of BV (r = 0.32, P = 0.0002) and tFHC (r = 0.42, P < 0.0001), which could help to discriminate multiple myeloma from monoclonal gammopathy of undetermined significance (tFHC mean ratio = 3.2; Mann-Whitney U-test, P < 0.0001). tFHC levels highly correlated with other disease activity markers, namely haemoglobin (r = -0.35; Spearman's rank, P = 0.0001), percentage of bone marrow plasma cells (r = 0.4, P < 0.0001) and beta2m levels (r = 0.36, P < 0.0001), while only the last barely correlated (r = 0.2, P = 0.03) with AV. Finally, the 0.4, 0.57 and 0.71 mg/l BV, tFHC and (to a lesser extent) FHC cut-off values divided patients into two groups with different survival curves (P = 0.0005, P = 0.0025 and P = 0.04 respectively). These data are in favour of a correlation between disease aggressiveness and cleavage of these variants by membrane-type metalloprotease enzymes.

Interferon-gamma drives the metalloproteinase-dependent cleavage of HLA class I soluble forms from primary human bronchial epithelial cells

Activation of bronchial epithelial cells (BEC) and disruption of an intact epithelial barrier in a lung transplant recipient can lead to acute or chronic rejection, events that are associated with release of soluble human leukocyte antigen (sHLA) class I. Although we know that HLA is released from mitogen-activated lymphocytes in a metalloproteinase (MPase)-dependent fashion, the mechanism of release from nonlymphoid tissue is not well understood. To this end, we stimulated primary BEC with increasing amounts of the T-helper cell-1 cytokines, interferon gamma (IFNgamma), and/or tumor necrosis factor alpha (TNFalpha) and measured the quantity and forms of HLA class I release. We found that IFNgamma, but not TNFalpha, was able to stimulate a time- and concentration-dependent release of HLA/beta(2)m and beta(2)m-free heavy chain (HC) from the BEC. A portion (50%) of the HLA/beta(2)m release and >90% of the beta(2)m-free HC release was mediated by a MPase. Western blot analysis supported the conclusion that a MPase-sensitive pathway produced 36 and 37 kDa cleaved forms, whereas the secreted 39 kDa form of beta(2)m-associated soluble HLA class I (sHLA/beta(2)m) was MPase-resistant. This adds to the growing understanding of the extracellular processing pathways of major histocompatibility complex class I that may be critical for both chronic rejection as well as immune regulation.

Human liver allograft acceptance and the "tolerance assay". II. Donor HLA-A, -B but not DR antigens are able to trigger regulation of DTH

In our initial study of liver transplant recipients using the trans vivo delayed-type hypersensitivity (DTH) assay, we found that in donor derived B-LCL or sonicates of donor leukocytes triggered linked suppression of the response to recall antigens tetanus toxoid (TT) or Epstein-Barr virus (EBV). Since both donor antigen sources contain HLA class I and class II proteins, we wished to determine which donor HLA proteins were responsible for the linked suppression effect. PBMC from four liver transplant recipients with donor-specific DTH regulation were studied. Surprisingly, we found that single donor HLA-A or B antigens (4/4 patients) but not single HLA-DR (0/4) donor antigens triggered linked suppression of DTH. A dose response study of two patients revealed that donor-type HLA-DR antigens (0.5-500ng) were not capable of triggering any linked suppression; however, as little as 500pg of donor-type HLA-class I protein triggered linked suppression of DTH response to a recall antigen. These findings may have implications for the differential impacts of class I vs class II mismatching in organ transplantation. On a practical level, they indicate that soluble HLA-A and B antigens are the proper choice for detection of DTH regulation as part of a "tolerance assay" in human liver transplant recipients.