Effect of HLA phenotype and gender on expression of various forms of class I HLA in plasma

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.

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

We determined the concentration of donor sHLA/beta(2)m and total beta(2)m-free heavy chain (HC) in the serum of lung transplant recipients with ELISA assays. While we were unable to detect specific donor beta(2)m-free HCs due to a lack of available antibodies, we could determine if events that led to an increase in the release of beta(2)m-free HC also led to an increase in the release of donor sHLA/beta(2)m, particularly the 36 kDa, proteolytically cleaved form. We found that lung transplants constituitively release donor sHLA/beta(2)m at ng/ml levels. The levels (both of donor sHLA/beta(2)m and total beta(2)m-free HC) were significantly increased in CMV-sero-negative recipients (but not in CMV-sero-positive recipients) at the onset of post-transplant CMV disease. Acute rejection episodes were also associated with an increased release of donor sHLA/beta(2)m, but not of beta(2)m-free HC. However, in patients with particularly poor outcome (i.e., graft loss within 1 year) there was a significant release of beta(2)m-free HC. Analysis of one such patient showed a predominance of 36 kDa forms of donor-sHLA/beta(2)m. Our data are consistent with the hypothesis that the metalloproteinase that cleaves beta(2)m-free HC is active during uncontrolled CMV infection and acute rejection. However, recall responses to CMV and controlled immune responses to donor may result in little or no activation of sHLA class I release.

Immunologic considerations for therapeutic strategies utilizing allogeneic hepatocytes: hepatocyte-expressed membrane-bound major histocompatibility complex class I antigen sensitizes while soluble antigen suppresses the immune response in rats

Understanding the immunologic effects of hepatocytes is critical because of the potential to use these cells for bioartificial livers, as a vehicle for gene transfer, and as a means to induce donor-specific immunosuppression in organ transplantation. However, this understanding is complicated by the fact that hepatocytes express membrane-bound and soluble forms of major histocompatibility complex (MHC) class I antigen, each with the potential to induce different immune responses. In the present study we first determined the immunologic effect of normal donor-derived hepatocytes in a rat heart transplant model. We then used ex vivo hepatocyte gene transfer to examine the immunologic effects of different forms of hepatocyte-expressed MHC class I antigen. Results showed that intrasplenic injection of purified, donor-strain-specific hepatocytes into recipients primes alloimmunity, as evidenced by acceleration of heart allograft rejection. Interestingly, injection of autologous hepatocytes transfected ex vivo with DNA encoding only membrane-bound donor MHC class I antigen (RT1.A(a)) also accelerated allograft rejection. However, hepatocytes transfected to express only secreted donor MHC antigen prolonged transplant survival. Limiting-dilution analysis of lymphocytes from animals treated with hepatocytes producing only secreted alloantigen showed an antigen-specific reduction in cytotoxic T lymphocyte (CTL) and helper T lymphocyte (HTL) precursors. Further analysis of CTL populations by flow cytometry revealed a relatively high percentage of nonviable cells, implying that soluble antigen promotes allospecific CTL death. In summary, this study suggests that hepatocyte-expressed MHC class I molecules have opposing immunologic effects, with the membrane-bound antigen inducing immunologic sensitization, and the soluble antigen promoting donor-specific immunosuppression.

Monitoring of soluble HLA class I size variants after liver transplantation

To monitor soluble HLA class I (sHLA-I) and their size variants after liver transplantation (LTX) plasma samples from 22 LTX patients were studied by sHLA-I ELISA, SDS-PAGE, and densitometry. Samples collected were classified into three groups: Group 1 comprised samples taken during episodes without complications, group 2 during episodes of cholangitis/cholestasis (CC), and group 3 during episodes of acute rejection (AR). Compared to group 1 (0.27 +/- 0.03 SEM microg/ml) mean sHLA-I increments in groups 2 and 3 were with 0.53 +/- 0.05 SEM microg/ml and 0.47 +/- 0.04 SEM microg/ml increased (p < 0.001). The same samples were studied by SDS-PAGE and the 43, 39, and 35 kD sHLA-I variants were quantified densitometrically. In samples of group 1 ratios of 43 vs. 39 kD bands revealed a mean of 2.1 +/- 0.3, whereas in group 2 and 3 these were only 0.8 +/- 0.1 SEM and 0.9 +/- 0.1 SEM, respectively, (p < 0.001). For the relation between 43 and 35 kD variants a reduced ratio of 1.1 +/- 0.2 SEM was confined to group 3 samples (p < 0.001), as groups 1 and 2 had ratios of 13.4 +/- 2.3 SEM and 8.4 +/- 2.9 SEM, respectively. This indicates that elevated sHLA-I levels during CC or AR are mainly caused by increases of 39 and/or 35 kD sized molecules. Therefore, our study demonstrates, that after LTX the contribution of sHLA-I size variants to total sHLA-I amounts changes drastically during immune activation pointing to different mechanisms of sHLA-I release.

Serum soluble human leucocyte antigen class I in paediatric liver transplantation with live, related donors

Serum soluble human leucocyte antigen (HLA) class-I is a useful marker for predicting immunological events in organ transplantation. In cadaver liver transplant cases it is especially the case that high amounts of soluble HLA-I are excreted from the grafts. In Japan, almost all liver transplants have been performed from living parent donors to their children. Therefore, it is interesting to know how soluble HLA-I changes in relation to clinical course. As part of this study we first examined serum concentrations of soluble HLA-I in 33 paediatric patients using enzyme-linked immunosorbent assay. Soluble HLA-I is composed of three different sized molecules (45, 39 and 34-36 kDa); then the change of distribution of these three molecules was demonstrated by Western blot analysis. When donor and recipient have different soluble HLA-I band patterns, the origin of the antigen can be assumed by this method. We found that in a comparison between pre- and post-transplants, the six out of eight (75%) patients that suffered episodes of acute rejection showed a significant elevation of soluble HLA-I, and all patients with infectious episodes had an elevated soluble HLA-I. Meanwhile, 10 out of 22 (45%) patients without any clinical complications still showed increased soluble HLA-I. The Western blot analysis showed that the soluble HLA-I molecules were considerably derived from the grafted liver, from one week to 24 months after grafting. In acute rejection, the band signals of donor origin were significantly increased. These signals were attenuated after immunosuppressive therapy. The grafted liver appears to contribute to the increase of soluble HLA-I following liver transplantation, and this increase is greater with the effects of the host immune system.

Soluble HLA class I antigens in patients with type I diabetes and their family members

Our objective was to study a possible contribution of MHC genes to S-HLA-I secretion in patients with Type I diabetes. Quantitatively, we used a highly sensitive enzyme-linked immunoassay to measure S-HLA-I in the serum of a total of 39 patients with Type I diabetes, as well as 36 kinships of 12 diabetic patients and 82 normal individuals with known HLA-phenotypes. S-HLA-I levels were abnormally elevated in patients or their non-diabetic relatives compared to normal controls (p < 0.0009). No complete HLA-haplotype had been identified to be correlated with high or low S-HLA-I secretion. Only the HLA-A23 or A24 (splits of HLA-A9) positive individuals sera were found to contain high S-HLA-I concentrations in all populations studied. The difference in S-HLA-I levels of HLA-A24 patients (n = 4) or their HLA-A24 positive non-diabetic relatives (n = 10) to the group of HLA-A24 normal controls (n = 15) was statistically highly significant (p < 0.0005 and p < 0.0009, respectively). The results suggests that HLA-A24 may confer additional independent risk for the disease expression in male children but not in female siblings. Nevertheless, the data implies that the patients or their non-diabetic relatives carrying the HLA-A24 have increased risk of developing ICA associated with high S-HLA-I levels compared to HLA-A24 negative probands or their kinships with low levels of S-HLA-I. This effect occurred irrespective to other diabetes related HLA-DR alleles. In summary, the results show a pronounced genetic heterogeneity of Type I diabetes with MHC control of the expression of S-HLA-I and possible involvement of hormonal factors that might potentiate a specific synthesis of S-HLA-I. The findings have implications for identifying individuals with a possible risk for developing the disease.

Induction of alternative splicing of HLA-B27 by bacterial invasion

OBJECTIVE

Alternative splicing of certain class I major histocompatibility complex pre-messenger RNA (pre-mRNA) is known to lead to generation of a cell-free soluble protein analog. This study was undertaken to examine whether this process occurs with HLA-B27, whether the process is modified by arthritis-causing bacteria, and whether the assembly of the soluble molecules follows the same pathway as the integral parent molecules.

METHODS

Alternative splicing of pre-mRNA was analyzed by reverse transcriptase-polymerase chain reaction, and assembly of soluble HLA-B27 by immunoprecipitation followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography.

RESULTS

There was alternative splicing of the pre-mRNA of HLA-B27. The process could be amplified by invasion with Salmonella or Yersinia bacteria. The soluble HLA-B27 was assembled in a pathway similar to that of the parent molecule.

CONCLUSION

The association between arthritis-causing bacteria and HLA-B27 positive cells is a complex event. Soluble HLA-B27 is a potential key player.

Quantification and molecular analysis of plasmatic HLA-BCw molecules with a locus B and Cw HLA specific mAb (B1.23.2 mAb)

Plasmatic HLA class I molecules were analysed quantitatively and qualitatively with a B and Cw locus-specific mAb, B1.23.2. sHLA-BCw were detected among all individuals with a wide range of concentration. The HLA-A29(19) allele was significantly associated with an increased sHLA-BCw mean concentration. Three different isoforms of relative molecular weights of 44, 39 and 36kDa were detected. The 39 kDa class I heavy chain was not detected after immunoprecipitation with mAb B1.23.2 in 17% of tested plasma, but was immunoprecipitated with W6/32 mAb.

Segregation study of the soluble 39-kD HLA class I heavy chain

To study the variable expression and inheritance of the 39-kD M(r) form of HLA class I molecules, we investigated the plasma of 12 families with 61 members and 41 unrelated individuals by SDS gel electrophoresis and class-I-specific immunoblotting. Seven families were informative for the presence and absence of the 39-kD band with a clear segregation pattern in coupling with HLA. The data were in agreement with a codominant expression of this molecular variant of sHLA class I. Of the 48 independent HLA haplotypes, 19 were identified as carrying the 39-kD deficiency. However, there was no clear association with HLA-B7 or gender. Under the assumption that all haplotypes in the five non-informative families carried the expressed 39-kD variant, approximately 40% of the Caucasian population should be heterozygous deficient for the 39-kD band of sHLA class I.

Quantitation and characterization of plasma HLA in neonates of different gestational ages

The functional significance of plasma HLA class I antigens is unclear. They are thought to have an immunomodulatory role and be tolerogenic in transplant settings including the materno-fetal semi-allograft. There is, however, no available data on the concentrations of soluble HLA class I antigens in fetuses or newborns. We therefore determined plasma HLA class I antigen levels in 93 neonates born at different gestational ages and compared them to those in 66 healthy adults. The mean plasma HLA concentration in cord blood obtained from these neonates (0.30 +/- 0.15 microgram/ml, mean +/- SD) was significantly lower (p < 0.0001) than in the adults (0.77 +/- 0.44 microgram/ml). No correlation between the plasma HLA levels and the gestational ages of the neonates was detected. Characterizing the plasma HLA class I antigens by immunoprecipitation and immunoblotting, four different molecular weight forms, 44, 39, 36 and 34 kDa, were recognized. Their distribution in neonates was not different from that in adults. Since the circulating leukocytes are a probable source of plasma HLA class I antigens, we measured the surface HLA expression on leukocytes in 4 neonates and 4 adults by immunofluorescent flow cytometry. The fluorescence intensities on neonatal granulocytes and lymphocytes were 50% of those on corresponding adult cells. This finding suggests that the reduced HLA expression by neonatal leukocytes may be partially responsible for the lower concentration of HLA class I antigens in neonatal plasma.

Typing of serum-soluble HLA-B27 antigen by ELISA

An ELISA using serum as soluble HLA antigen source was developed for HLA-B27 typing. Two sandwich assays were run in parallel. The first assay utilized a monoclonal antibody (mAb) reacting with a determinant expressed by both HLA-B7 and B27 antigens; the other assay utilized a mAb reactive with HLA-B7 antigens but not with HLA-B27 antigens. After incubation with serum samples, bound HLA antigen was detected using an anti-beta 2m antibody conjugated to peroxidase and a chromogenic substrate. Absorbance of each well was measured at 490 nm. Based on analysis of absorbances obtained with panels of specimens of known HLA phenotypes, a mathematical algorithm was developed to derive the specimen HLA-B27 phenotype from its ELISA absorbance values. Despite the lack of monospecific mAb, an accurate HLA-B27 typing was possible. 362 specimens (including 151 HLA-B27-positive) were tested. Agreement between microlymphocytotoxicity and ELISA was 99.2%. No correlation between the level of HLA-B27 antigen reactivity and the amount of total HLA class I antigen in serum was observed. This report demonstrates the possibility of using serum-soluble HLA antigen and ELISA technology for histocompatibility testing. The assay offers several significant advantages over microlymphocytotoxicity: no need for cell preparation, batch testing capabilities and objective, reproducible interpretation of results.