Quantitation of soluble HLA class II molecules by an enzyme-linked immunosorbent assay

Human Leucocyte Antigen Sensitisation and Its Impact on Transfusion Practice

Human leucocyte antigen (HLA) sensitisation, including the formation of antibodies against HLA, can cause serious effects in patients receiving blood. Under certain circumstances, donor HLA antibodies in the blood product can trigger the patient's granulocytes to release mediators that cause transfusion-associated lung injury (TRALI), a serious complication of transfusion. The HLA systems of both donor and patient are involved in transfusion-associated graft-versus-host disease, which is a rare disease with a high mortality. Patient HLA antibodies can destroy incompatible platelets and may cause refractoriness to platelet transfusion. Identification of a patient's HLA antibody specificities is necessary for issuing compatible platelets to overcome refractoriness. Many techniques for the detection and identification of HLA antibodies have been developed, including complement-dependent cytotoxicity assay, bead-based assays, the platelet adhesion immunofluorescence test, and the monoclonal antibody-specific immobilisation of platelet antigens assay. Different strategies for the selection of HLA-compatible platelets are applied. These strategies depend on the breadth of antibody reactivity and range from avoiding single HLA antigens in the platelet concentrates issued to apheresis of platelets from HLA-identical donors. The mechanisms of HLA sensitisation and the efforts made to provide compatible blood products to sensitised patients are reviewed in this article from the perspective of clinical transfusion medicine.

Allostimulatory capacity of conditionally immortalized proximal tubule cell lines for bioartificial kidney application

Novel renal replacement therapies, such as a bioartificial kidney (BAK), are needed to improve current hemodialysis treatment of end-stage renal disease (ESRD) patients. As BAK applications may reveal safety concerns, we assessed the alloimmunization and related safety aspects of readily available conditionally immortalized human proximal tubule epithelial cell (ciPTEC) lines to be used in BAK. Two ciPTEC lines, originally derived from urine and kidney tissue, were characterized for the expression and secretion of relevant molecules involved in alloimmunization and inflammatory responses, such as HLA class-I, HLA-DR, CD40, CD80, CD86, as wells as soluble HLA class I and proinflammatory cytokines (IL-6, IL-8 and TNF-α). A lack of direct immunogenic effect of ciPTEC was shown in co-culture experiments with peripheral blood mononuclear cells (PBMC), after appropriate stimulation of ciPTEC. Tight epithelial cell monolayer formation on polyethersulfone flat membranes was confirmed by zonula occludens-1 (ZO-1) expression in the ciPTEC tight junctions, and by restricted inulin-FITC diffusion. Co-culture with (activated) PBMC did not jeopardize the transepithelial barrier function of ciPTEC. In conclusion, the absence of allostimulatory effects and the stability of ciPTEC monolayers show that these unique cells could represent a safe option for BAK engineering application.

Soluble human leukocyte antigen: A diagnostic indicator of rheumatoid arthritis?

Early stage rheumatoid arthritis (RA) is often difficult to diagnose because initial symptoms are non-specific. To aid diagnosis, suitable serological diagnostic markers are sought. Elevated levels of soluble MHC class II (soluble human leukocyte antigen; sHLA-DR) in human serum have been associated with rheumatoid and 'rheumatoid-like' autoimmune diseases. As a result, sHLA-DR has been suggested as a specific marker of RA. However, reported levels of sHLA-DR in sera of healthy donors vary significantly and the mechanism of release of HLA-DR into serum is poorly understood. Investigations into the diagnostic potential of this molecule necessitate the development of a sensitive and specific sHLA-DR assay. We have investigated multiple ELISA setups to develop such an assay and false positive signal has been carefully removed using a combination of isotype-matched controls and immuno-depletion. sHLA-DR levels in sera of RA patients were not significantly different from those in healthy donors which suggests sHLA-DR has limited utility in the diagnosis of RA. In RA patients, we detected high levels of sHLA-DR in aspirated synovial fluid (SF), but this did not correlate with sHLA-DR levels in serum.

Soluble HLA-DR levels in serum are associated with therapy and genetic factors in rheumatoid arthritis

As rheumatoid arthritis (RA) is an HLA-DR associated autoimmune disease and soluble HLA-DR (sHLA-DR) molecules have the capacity to regulate the immune response, we studied the sHLA-DR levels in RA patients in view of therapy modalities and clinical and biologic parameters of disease activity. For this sHLA-DR concentrations from 87 RA patients were determined by a sensitive enzyme-linked immunoabsorbent assay (ELISA) format. There was a weak but significant correlation between sHLA-DR levels and disease activity (r 0.186 to 0.287, p < 0.004 to < 0.001). The mean serum sHLA were not significantly different between groups with or without corticosteroids, or undergoing therapy with different disease modifying antirheumatic drugs. However, patients treated with a combination of methotrexate and prednisolone have lower sHLA-DR (206 +/- 21 ng/ml, n = 34) compared with the mean value for all other samples (306 +/- 16, n = 217, p < 0.001). This corresponded with significantly lower EULAR pain and swelling scores, ESR and rheumatoid factor (RF) by latex fixation (p < 0.02 to 0.001) in the former, compared with the latter group. Furthermore, sHLA-DR was, respectively, 267 +/- 15 ng/ml (n = 182) in samples from patients treated with nonsteroidal anti-inflammatory drugs (NSAIDs), and 358 +/- 31 (n = 72) without NSAIDs (p < 0.01). Lower sHLA-DR with NSAIDs contrasted with significantly higher scores for pain, swelling, CRP, and RF by latex fixation and by Waaler-Rose test (p < 0.05 to 0.001). Comparison of subgroups with or without the shared epitope of RA disease (Q)R/KRAA within the HLA-DR beta1-chain confirmed significantly higher parameters of disease activity and sHLA-DR in the presence of this disease associated epitope in our patients. Different mechanisms appear to be involved in sHLA-DR production or release, as their level correlates positively with disease activity under combined therapy with corticosteroids and methotrexate, but decreases with higher disease activity in patients treated with NSAIDs.

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.

Serum soluble HLA-DR antigens in autoimmune hepatitis

To investigate the significance of HLA-class II, especially DR antigens, in autoimmune hepatitis (AIH), the serum concentrations of soluble HLA-DR antigen (sDR) were measured in 16 patients with AIH. The expression of HLA-DR antigens in the liver tissues of AIH patients was also studied by immunohistochemistry. AIH at diagnosis showed markedly higher serum sDR levels than controls, in which the liver tissues exhibited positive staining of HLA-DR antigens. Seven patients received corticosteroid therapy, in whom the serum sHLA-DR concentration was reduced dramatically from activated to remission stage. In sequentially follow-up cases, sDR correlated well with the disease activity, and also with the change of surface DR expression in the liver. A single major band with a molecular size of 60 kDa was detected, both in patient's sera and in normal control sera, by Western blotting. In conclusions, serum sHLA-DR level could be a marker reflecting immunological activity of the disease.

Soluble HLA in human body fluids

There is a growing body of information about the soluble forms of HLA in serum but there are only a few reports discussing sHLA in other body fluids. We quantitated sHLA-I and sHLA-II concentrations in sweat, saliva and tear samples from five normal individuals with known HLA-phenotypes. We also studied sweat samples from an additional 12 normal nonphenotyped subjects, as well as in CSF of 20 subjects with different illnesses, using solid phase enzyme linked immunoassay. Sweat, saliva and tears from normal subjects were found to contain very low or nondetectable amounts of sHLA-I. In contrast, sHLA-II molecules were found in each of these body fluids, although, with considerable variation between individuals. The presence of sHLA-II in saliva was further confirmed by Western-blotting. It was observed that sHLA-II having molecular mass of 43,900 and 18,100 daltons was comparable with that found in serum from normal individuals. In addition, no association of sHLA-II levels with allospecificities in either body fluid or in serum was apparent. The results of CSF sHLA concentrations in different diseases were as follows: (1) High CSF SHLA-I levels were measured during viral encephylitis (n = 3), while none of these patients contained sHLA-II in CSF; (2) The levels of sHLA-II, but not sHLA-I were elevated in CSF of patients during seizure (n = 6) and of patients with neonatal hepatitis (1 of 2) or with connective tissue disease accompanied with viral infection (n = 2); (3) No CSF sHLA-I or sHLA-II could be detected at polyneuropathy (n = 2), or in patients with syphilis (n = 3), or leukemia (n = 2) with evidence of neurologic involvement of central nervous system. Taken together, it may be concluded that the presence of sHLA in several body fluids is physiologically normal. It appears that sHLA-II is the predominant class of HLA molecules present in different body fluids. We propose that the system responsible for sHLA-II production in various body fluids must involve different mechanisms than those responsible for sHLA-I synthesis in serum.

B-cell antigens within normal and activated human T cells

In this study we compared cell surface staining for human peripheral blood lymphocyte (PBL) CD antigens by flow cytometry, with staining obtained following permeabilization of PBL using the Cytoperm method (Serotec). Six CD antigens (CD20, CD21, CD22, CD32, CD35 and major histocompatibility complex class II antigen) normally found on the surface of B cells, were also found to be expressed within T cells. We also showed, by immunoelectron microscopy, that these inappropriately expressed ('occult') CD antigens are located within cytoplasmic vesicles or within the rough endoplasmic reticulum. Following in vitro activation of T cells a distinct increase in expression of all of these cytoplasmic antigens was observed but staining at the cell surface was, by comparison, weak. We therefore propose that up-regulation of various B-cell CD antigens occurs within the cytoplasm of T cells following activation and that these antigens may be synthesized and released into the fluid-phase as soluble immunoregulatory molecules.

Soluble HLA class I and class II antigens in patients with multiple sclerosis

Soluble HLA class I (sHLA-I) and soluble HLA class II (sHLA-II) antigen levels during different stages of disease were investigated in paired serum and cerebrospinal fluid (CSF) samples from 37 patients with multiple sclerosis (MS) using ELISA and Western blot analysis. Soluble HLA-II antigens in the serum of untreated patients with the relapsing-remitting type of MS (RRMS) were found to be significantly elevated in acute relapse as compared to values obtained from patients under steroid treatment, in remission or healthy controls. No significant differences in circulating sHLA-I levels could be detected. In contrast, a trend towards increased intrathecal production of sHLA-I molecules in the CSF was observed in untreated RRMS patients in acute relapse, whereas the levels of soluble HLA-II antigens in the CSF were below the detection limit of the ELISA method. Our observations underline the presence of systemic immune activation in MS patients, as reflected in elevated serum sHLA-II antigen levels, and reveal a dichotomy between sHLA class I and II antigen production in the peripheral blood versus CSF in acute MS. Serial measurements of sHLA-II antigen levels might represent a non-invasive method to assess disease activity in MS patients.

Soluble human leukocyte antigens, interleukin-6, and interferon-gamma during pregnancy

PROBLEM

Soluble human leukocyte antigens (sHLA), interferon-gamma (IFN-gamma), and interleukin-6 (IL-6) were studied during human pregnancy to test the hypothesis that sHLA concentrations are regulated by these specific cytokines.

METHOD OF STUDY

Enzyme-linked immunoadsorbent assays (ELISA) were used to measure sHLA I and II in maternal circulation, cord blood, and placenta effluents of pregnant and nonpregnant women; maternal serum cytokines were also determined.

RESULTS

sHLA in maternal and cord blood were equivalent to that in the placenta. By the third trimester, sHLA I concentrations in maternal plasma were significantly reduced compared to the first or second trimesters. sHLA II was increased during the second trimester relative to that postpartum. Maternal IL-6 and IFN-gamma concentrations were not statistically different throughout gestation or postpartum.

CONCLUSIONS

These data do not suggest a role for maternal plasma IL-6 or IFN-gamma in regulation of systemic sHLA class I during pregnancy, but they do not address whether such events take place in local tissues of the maternal-fetal unit.

Biochemical analysis of plasma-soluble invariant chains and their complex formation with soluble HLA-DR

The invariant chain (CD74) is preferentially localized in the cytoplasm and regulates the loading of exogenous derived peptides into HLA class II heterodimers. In addition, a small proportion of CD74:class II complexes is also expressed on the cell surface. We identified and quantified soluble CD74 (sCD74) molecules in the plasma and sCD74:sHLA-DR complexes by ELISA. EDTA plasma samples from 86 healthy probands were analyzed. sCD74 could be detected in all samples with a mean concentration of 1.14 relative units +/- 1.04 SD (range 0.17-4.31). Approximately 10% of the samples had increased amounts of sCD74 (>3.0 relative units). Complexes of sCD74 and sHLA-DR were detected in all samples and their quantities were positively correlated (r=0.83, p<0.001) with the sCD74 concentrations. SDS-PAGE analysis of plasma samples with high sCD74 concentrations (>3.0 relative units) revealed four isoforms of sCD74 with molecular weights of 45, 43, 35, 31 kDa corresponding to known sizes of intracellular CD74. However, only molecular weights of the 45 and 43 kDa isoforms of sCD74 are found complexed with sHLA-DR. Our data demonstrate, that CD74 molecules are present in their soluble form in the plasma of healthy probands and form complexes with soluble HLA-DR molecules.

Soluble HLA class I and class II molecule levels in serum and cerebrospinal fluid of multiple sclerosis patients

Increased concentrations of soluble HLA class I and class II molecules (sHLA-I and sHLA-II) have been observed in infectious, inflammatory, and autoimmune diseases. Because autoimmune mechanisms are considered to play a role in the pathogenesis of multiple sclerosis (MS), we decided to dose sHLA-I and sHLA-II in serum and cerebrospinal fluid (CSF) of MS patients comparing their concentrations with those observed in serum and CSF of patients with other neurologic diseases (OND) without evidence of neuroradiologic involvement of central nervous system (CNS) and in serum of healthy donors. The serum concentrations of sHLA-I were higher in both MS and OND patients than in healthy donors (P < 0.05) whereas sHLA-II serum concentrations were lower in MS patients than in both OND patients and healthy donors (P < 0.01). Detectable amounts of sHLA-II were observed in the CSF of 45% of MS patients and in CSF of only 6% of OND patients (P < 0.001). In MS patients a significant correlation between sHLA-I serum and CSF concentrations was observed (P < 0.01), whereas sHLA-II serum and CSF levels did not correlate. In conclusion, alterations of sHLA-I and sHLA-II serum and CSF concentrations are present in MS patients and could be involved in the induction of enhanced susceptibility to develop MS or in MS pathogenesis.

Serum and urine soluble HLA class I antigen concentrations are increased in patients with hemorrhagic fever with renal syndrome

OBJECTIVES

In order to evaluate the association between the Hantaan virus-induced cellular-immune response and clinical severity in patients with hemorrhagic fever with renal syndrome (HFRS).

METHODS

We serially measured the serum (n = 16) and urine (n = 6) concentrations of soluble HLA class 1 antigen (sHLA-l) and clinical powameters in patients with HFRS.

RESULTS

Serum sHLA-I concentrations in patients with HFRS were significantly higher than those in controls throughout all clinical phases (p < 0.01). The highly elevated Serum sHLA-I concentrations peaked in the oliguric phase and declined gradually through the phases of HFRS. Serum sHLA-l concentrations in patients with hypotensive episode were higher than in those without the episode (5,85 +/-2,184 vs. 2,389 +/- 860 ng/ml in oliguric phase, 4.11 +/- 1,952 vs. 1,502 +/- 592 ng/ml in diuretic phase, p < 0.05), and serum sHLA-l levels showed a significant correlation with blood WBC count (r = 0.75 in the febrile and hypotensive phase, p < 0.01) and serum creatinine concentrations (r = 0.64 in the oliguric phase, p < 0.01), respectively, Urine sHLA-I levels in the oliguric phase were significantly higher than those in the diuretic phase (390 +/- 155 vs. 214 +/- 45 ng/mg Cr, p < 0.05) and urine sHLA-I levels are associated with severe illness in patients with HFRS. The higher serum sHLA-I are associated with severe illness in patients with HFRS. The persistent elevation of serum sHLA-I during all phases of HFRS might be related to increased production due to prolonged cellular immunologic stimulation by the Hantaan virus rather than decreased excretion of sHLA-I through the kidney.

CONCLUSION

We suggest that the serum and urine sHLA-I concentrations can be used as a stable and objective parameter for monitoring clinical severity and renal dysfunction in patients with HFRS.

Influence of anticoagulants on the level of soluble HLA class I and class II antigens measured in blood samples

The existence of soluble forms of HLA class I and class II antigens in human serum is well established and altered concentrations of these serum proteins have been described to be associated with various diseases. Since soluble HLA antigens (sHLA) can be measured both in serum and plasma samples, we investigated whether anticoagulant treatment influences the determined levels of soluble HLA class I (sHLA-I) or soluble HLA-DR (sHLA-DR). Analyzing paired samples of serum and plasma of 40 healthy individuals we found significantly lower serum levels of sHLA-DR (0.31 +/- 0.15 ng/ml) compared to EDTA plasma levels (0.58 +/- 0.20 ng/ml). By contrast, serum levels of sHLA-I (0.89 +/- 0.74 micrograms/ml) were only slightly lower than EDTA plasma values (0.95 +/- 0.86 micrograms/ml), a situation similar to that of sIL-2R and sCD4 levels. Further experiments intended to clarify the reasons of the reduced sHLA-DR serum levels revealed that (i) the blood storage time before centrifugation did not influence the sHLA-DR level, (ii) treatment of serum with anticoagulant did not augment the measured sHLA-DR concentration, and (iii) the recovery of spiked sHLA-DR was significantly lower when added to native blood than to serum or anticoagulant-treated blood. These results suggest that sHLA-DR is partly removed by the process of blood clotting thus resulting in diminished sHLA-DR serum levels.

Increased serum concentration of soluble HLA-DR antigens in HIV infection and following transplantation

HLA class I and class II antigens circulate in serum as soluble molecules. Increased concentrations of soluble HLA class I molecules have been demonstrated in viral diseases, in rejection episodes following organ transplantation and in graft versus host disease. To explore the possibility of a variation of the serum concentrations of soluble HLA class II molecules in the same pathologic conditions we developed a double determinant immune assay that detects whole soluble HLA-DR molecules (sHLA-DR). The mean level of sHLA-DR antigens in sera from 23 healthy individuals was 0.64 +/- 0.72 microgram/ml. Elevated serum concentrations of sHLA-DR molecules were detected in sera from HIV infected patients in CDC2/3 and in CDC4 C1 stages (2.0 +/- 1.7 micrograms/ml and 4.6 +/- 1.7 micrograms/ml, respectively), in sera from patients affected by acute rejection after liver transplantation (5.3 +/- 3.7 micrograms/ml) and in sera from patients affected by severe acute graft versus host disease following bone marrow transplantation (8.8 +/- 3.1 micrograms/ml). The increase of sHLA-DR molecules in these sera significantly correlated with the elevation of soluble HLA class I antigens (P = 0.0004). The reported data suggest that both soluble HLA class I and class II molecules serum levels increase during viral infections and strong immune reactions and could suggest the involvement of these molecules in immunoregulation.

Soluble HLA class I and class II concentrations in factor VIII and PCC preparations

Soluble HLA class I (sHLA-CI) and class II (sHLA-CII) molecules were quantitated in 11 commercially available factor VIII and prothrombin complex concentrate (PCC) preparations by enzyme-linked immunosorbent assays (ELISA). In 4 preparations, we detected traces of sHLA-CI (0.01-0.07 mg/l), and in 7 hemostatic preparations small amounts of sHLA-CII molecules (0.02-0.28 mg/l). The concentrations of these contaminant molecules are unequivocally below the mean values of sHLA in human plasma (sHLA-CI: 1.01 +/- 0.72 mg/l; sHLA-CII: 1.53 +/- 2.44 mg/l). Based on the total amount of chronically administered factor VIII or PCC, contaminating sHLA molecules may be in principle able to exert immunomodulatory effects in patients treated with such preparations.

Summary report from the first international workshop on soluble HLA antigens. Paris, August 1992

The First International Workshop on Soluble HLA antigens focused on the comparison of immunoassay procedures for quantitation of soluble HLA (sHLA) class I antigens and the selection of a sHLA class I antigen international standard. Several sets of serum, plasma, and cell culture supernatant specimens were assayed blindly for levels of sHLA class I antigens by 15 participating laboratories using different immunoassay formats. The sandwich ELISA using (i) for antigen capture: an anti-HLA class I heavy chain monoclonal antibody (mAb) specific for a monomorphic epitope, and (ii) for antigen detection: an anti-beta 2 microglobulin antibody-enzyme conjugate, was the assay format of choice. There was a high inter-laboratory correlation among the majority of laboratories. All serum and plasma specimens from normal donors, and from a single transplant patient, had detectable levels of sHLA class I antigens. Paired serum and plasma specimens had similar levels of sHLA class I antigens, although plasma sHLA antigens seemed more stable than serum sHLA antigens. sHLA-A2 and sHLA-B7 antigens were detected in all specimens from HLA-A2 and HLA-B7 donors, respectively, using allele-specific ELISAs. No difference in reactivity was observed for quantitation of native sHLA class I antigens whether the capture mAb was TP25.99 (alpha 3 domain-specific) or W6/32 (alpha 2 + alpha 3-specific). However, a human-mouse chimeric sHLA class I antigen reacted weakly in assays which used TP25.99 mAb. The wide variation among laboratories in their reporting of micrograms/ml units pointed to the need for an inter-laboratory standardization based on a calibrated sHLA antigen preparation. T.sB7, an sHLA-B7 antigen derived from a cell line transfected within human beta 2 microglobulin and HLA-B7 genes, was accepted as the First sHLA class I Antigen International Standard at the workshop meeting.

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.

Soluble CD4, CD8, and HLA molecules in commercial immunoglobulin preparations

CD4 and CD8 exist in membrane-bound and soluble forms. These antigens are the physiological ligands for molecules of HLA classes I and II, which we have found in soluble form in commercial immunoglobulin preparations. We measured concentrations of soluble CD4 and CD8, as well as soluble HLA-ABC and HLA-RQP in sixteen immunoglobulin preparations by enzyme immunosorbent assays. Only two preparations contained detectable CD8, and nine had soluble CD4 in varying amounts. There was great variation in concentrations of soluble HLA molecules. It is possible that the immunomodulating effects of immunoglobulin therapy in disorders with immune aetiology are due, at least partly, to these contaminating molecules.

Soluble HLA class I and class II concentrations in commercial immunoglobulin preparations

Soluble HLA class I (sHLA-ABC) and class II (sHLA-RQP) molecules were quantitated in 16 commercially available immunoglobulin (Ig) preparations by enzyme-linked immunosorbent assays. Whereas three Ig preparations contained no detectable sHLA-ABC, all preparations showed concomitant sHLA-RQP molecules. There was a considerable variability with regard to the individual sHLA concentrations. For sHLA-RQP the values exceeded that found in human plasma of healthy individuals, suggesting that the extraction procedure may concentrate not only Ig, but also HLA class II molecules. Based on the total dosage of intravenously administered immunoglobulins (i.v.Ig), contaminating sHLA molecules may become immunogenic. Furthermore, sHLA molecules are discussed in terms of participation in the well-known immunomodulating effects of i.v.Ig therapy.