A ribosomal protein of Yersinia pseudotuberculosis having partial epitope identity with HLA-B27

Antikörper gegen humane Leukozytenantigene (HLA) bei männlichen Apheresespendern ohne klassische Alloimmunisierung

Im Rahmen von Präventivmaßnahmen zur Vermeidung von TRALI (transfusionsassoziierte akute Lungeninsuffizienz) wurden in einer Studie 15 523 männliche und weibliche Apheresespenderinnen und -spender mit und ohne positiver Immunisierungsanamnese (IA) auf HLA-Klasse-I-, HLA-Klasse-II- und HNA-Antikörper (AK) untersucht. Unsere Ergebnisse zeigten, dass bei 3,85% der männlichen Spender ohne IA HLA-AK und bei 0,10% HNA-AK auftraten. Diese Beobachtung stellt die seit Beginn der HLA-Ära vor 50 Jahren klar bewiesene Aussage infrage, dass HLA-AK nur durch eine Alloimmunisierung infolge von Schwangerschaften, Transfusionen oder Transplantationen entstehen können. Wir diskutieren mehrere mögliche Kausalitäten dieser positiven Reaktionen:

Große Aufmerksamkeit richteten wir auf den Ausschluss möglicher falsch positiver Reaktionen, da der LABScreen Multi als höchst sensitiv eingeschätzt wird. Nach Validierung eines neuen positiven Normalized-Background-Cut-offs (NBG: Normalized Background) und der Nachtestung von Rückstellproben der als positiv getesteten männlichen Spender konnten 50% der HLA-Klasse-I- und 43% der HLA-Klasse-II-AK nicht bestätigt werden. Dennoch blieben 1,5% der getesteten männlichen Spender für HLA-Klasse I und 0,5% für HLA-Klasse II positiv. Handelt es sich hier ausschließlich um HLA-spezifische oder um heterophile AK? Welche klinische Bedeutung haben diese AK bei der Prävalenz von TRALI oder für die Transplantationsimmunologie?

Denatured class I human leukocyte antigen antibodies in sensitized kidney recipients: prevalence, relevance, and impact on organ allocation

BACKGROUND

Single antigen flow beads assays may overestimate sensitization because of the detection of supposedly irrelevant antibodies recognizing denatured class I human leukocyte antigens (HLAs).

METHODS

Sera of 323 HLA-sensitized kidney transplant candidates positive with a class I HLA single antigen flow beads assay were retested after acid treatment of the beads. Denatured HLA antibodies were identified according to ratio between the measured fluorescence intensity for treated and nontreated beads. T-lymphocyte flow cytometry crossmatches were performed to characterize the ability of these antibodies to recognize HLA on normal cells as a surrogate of their potential clinical relevance. Their impact on organ allocation was evaluated through a calculated panel reactive antibody. The utility of single antigen flow beads largely devoid of denatured HLA (iBeads) was also evaluated.

RESULTS

Denatured HLA antibodies were detected in 39% of the patients. They provided much less positive flow cytometry crossmatches than anti-native HLA antibodies (16% vs. 83%, P<0.0001). Removing the HLA-A and HLA-B antigens targeted by denatured HLA antibodies from unacceptable antigens lowered the calculated panel reactive antibody for 90 patients, sometimes dramatically. The iBeads assay demonstrated nearly the same ability to predict crossmatch results than the acid treatment assay.

CONCLUSION

Denatured class I HLA antibodies are common, but the antigens they target should not be considered as unacceptable in most cases, because they negatively impact access to a transplant while predominantly providing negative sensitive crossmatches. The iBeads assay seems to be a valuable alternative to better define unacceptable antigens.

Antibodies to HLA-E in nonalloimmunized males: pattern of HLA-Ia reactivity of anti-HLA-E-positive sera

Natural anti-HLA Abs found in sera of healthy nonalloimmunized males recognize HLA-Ia alleles parallel to those recognized by anti-HLA-E mAbs (MEM-E/02/06/07). Therefore, some of the HLA-Ia Abs seen in healthy males could be due to anti-HLA-E Abs cross-reacting with HLA-Ia. If anti-HLA-E Abs occur in healthy nonalloimmunized males, it can be assessed whether they evoke HLA-Ia reactivity as do mouse HLA-E mAbs. IgG and IgM Abs to HLA-E and HLA-Ia alleles are identified in sera of healthy males using microbeads coated with recombinant denatured HLA-E or a panel of rHLA-Ia alleles. The pattern of allelic recognition is comparable to that of anti-HLA-E mAbs. Sixty-six percent of the sera with HLA-E IgG have a high level of HLA-Ia IgG, whereas 70% of those with no anti-HLA-E Abs have no HLA-Ia Abs. HLA-E IgM/IgG ratios of sera are divided into four groups: IgM(Low)/IgG(Low), IgM(High)/IgG(Low), IgM(High)/IgG(High), and IgM(Low)/IgG(High). These groups correspond to anti-HLA-Ia IgM/IgG ratio groups. When HLA-E IgM and IgG are absent or present in males, the IgM or IgG of HLA-Ia are similarly absent or present. The mean fluorescent intensity of HLA-Ia Abs correlates with that of anti-HLA-E Abs. Most importantly, HLA-E and HLA-Ia reactivities of the sera are inhibited by the shared, but cryptic, peptide sequences (117)AYDGKDY(123) and (137)DTAAQIS(143). Therefore, Abs to the H chain of HLA-E may be responsible for some of the HLA-Ia allele reactivity of the natural HLA-Ia Ab in human sera. Absence of any anti-HLA-Ia Abs in 112 nonvegans and the presence of the same in vegans suggest that dietary meat proteins might not have induced the natural allo-HLA Abs.

HLA-B27 determination using serological methods. A comparison of enzyme immunoassay and a microlymphocytotoxic test with flow cytometry and a molecular biological assay

Typing for HLA-B27 is routinely performed in patients with seronegative spondarthritides. Besides the microlymphocytotoxic test (MLCT), other serological techniques have been developed such as enzyme immunoassays (EIA) using serum or plasma as a source for the determination of soluble HLA-B27 (sHLA-B27) and flow cytometric (FC) methods. The aim of the present study was to check the accuracy and reliability of the EIA for sHLA-B27 in comparison to the MLCT using antibodies against HLA-B27 and cross-reacting specificities (CRS), as well as an FC method and a molecular biological method. Any discrepant results should be typed with the MLCT using a complete panel of anti-HLA-class I antibodies, with FC and with a molecular biological technique. The EIA should also be repeated in those patients, using serum and plasma from a new venipuncture. In 81 patients with rheumatic disorders, the EIA and the MLCT using antibodies against HLA-B27 and CRS were performed. Based on the MLCT with a complete panel of anti-HLA-class I antibodies as a standard, discrepant test results were obtained for 9 out of 81 patients with the MLCT using antibodies against HLA-B27 and CRS and with the EIA. The following wrong results occurred: in the MLCT with anti-HLA-B27 and CRS, there were two false-negative results; in the EIA there were four false-negative and one false-positive results; one sample was undeterminable. In comparison with the MLCT, including the complete panel of HLA-class I antibodies, as well as with a molecular biological technique, typing with FC showed a complete concordance. Our investigations demonstrated that for routine typing for HLA-B27 the MLCT cannot be replaced by EIA because of a significant number of mistypings. The MLCT performed only with antibodies against HLA-B27 and CRS may also lead to typing errors. No errors were detected using flow cytometry. If only serological methods can be performed in a laboratory a combination of flow cytometry and MLCT could therefore enhance the safety of HLA-B27 typing.

Seroreactivity to bacterial antigens is not a unique phenomenon in patients with autoimmune thyroid diseases in Canada

It has been suggested elsewhere that the enteric pathogen Yersinia enterocolitica (Y.e.) might be implicated etiologically in autoimmune thyroid disease (AITD). To reevaluate this hypothesis in the Canadian population, where the prevalence of anti-Y.e. antibodies in the general population is very low (< 1%), we have studied the occurrence of antibacterial reactivity (against Y.e. 0:3 and 0:9, Escherichia coli and Staphylococcus aureus) in the sera of patients with Hashimoto's thyroiditis (HT), Graves' disease (GD), nontoxic nodular goiter (NTG), and autoimmune rheumatic diseases (ARD) as well as normal controls (C). Using the tube agglutination method, no single positive sample was detected in these subjects. No differences in the mean levels of anti-Y.e. 0:3 or 0:9 by ELISA were observed between various groups of patients. Immunoreactivity in the course of medical therapy during 5-12 months did not show significant changes in any of 12 ARD and AITD patients. Some serological reactivity to the plasmid containing strain of Y.e. 0:3 was demonstrated in all subjects by the Western blotting technique. However, weaker signals and fewer bands were noticed in these sera compared to sera from patients with acute yersiniosis. Analysis of the pattern of reactivity did not show any difference in reactivity to any protein between the groups of subjects. The immunodominant antigen in Y.e. 0:3 to which IgG reacted in almost all subjects was the plasmid encoded 240-kDa protein. Our study favors the view that there is a merely coincidental incidence of seroreactivity to bacterial antigens, which appears to be irrespective of diagnosis.

Failure of the serological determination of HLA-B27 due to antigen masking in patients with ankylosing spondylitis

In patients suffering from ankylosing spondylitis (AS) HLA-B27 determination by means of the microlymphocytotoxicity test (MLCT) sometimes gives equivocal or false-negative results even though it has been performed with meticulous care. These failures of the test did not arise when the isolated mononuclear cells (MNC) were incubated in lymphocyte culture medium at 37 degrees C under sterile conditions for 24 h. To objectify these observations two methods of HLA class I typing were implemented before and after incubation of the test MNC in culture medium: a bioluminescence method based on the loss of adenosine triphosphate (ATP) in lysed cells in a modification of the usual MLCT and a flow cytometric (FC) test using direct immunofluorescence with an anti-HLA-B27 monoclonal antibody (MAB). In this study 50 patients with AS and 12 healthy volunteers were typed by the usual MLCT according to the NIH standard method and with both of the quantitative methods. In most of the AS patients the discrimination between positive and negative typing results became more distinct after 24 h incubation in culture medium. In the entire group of AS patients tested three false-negative typing results were prevented by this method. Although the MAB against HLA-B27 is cross-reactive with HLA-B7 and HLA-B22, errors in the FC analysis could be avoided by calibration of the flow cytometer with standard calibration beads. Possible explanations for masking of the HLA-B27 in AS patients are discussed.