Antibody reactivity to HLA classes I and II in sera from patients with hydatidosis

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-E monoclonal antibodies recognize shared peptide sequences on classical HLA class Ia: relevance to human natural HLA antibodies

The non-classical HLA-Ib molecule, HLA-E share several peptide sequence similarities with the heavy chains of classical HLA class Ia (-B and -C) molecules. Therefore, the antibodies to HLA-E, that recognize shared sequences, may bind to HLA-Ia alleles. This hypothesis is tested by examining the affinity of HLA-E monoclonal antibodies (HLA-E-MAbs) to HLA-Ia molecules and by inhibiting the antibody binding to both HLA-E and HLA-Ia with the shared peptide sequence(s). Single recombinant HLA molecule-coated beads are used for antibody binding. The antibody binding is evaluated by measuring mean fluorescence index [MFI] with Luminex multiplex flow-cytometric technology. The peptide-inhibition experiments are carried out with synthetic shared peptides, most prevalent to HLA-E and HLA-Ia alleles. The number of HLA-Ia alleles recognized by the HLA-E-MAbs varies with the density of the antigen (quantity of antigen-coated beads) and dilution of MAb. Binding of HLA-E-MAbs to beta2 microglobulin (beta(2)m)-free HLA-Ia antigens confirms the location of the epitopes on the heavy chain (HC) of the antigens. Strikingly, the nature of alleles of HLA-Ia recognized by different HLA-E-MAbs is identical. The binding of HLA-E-MAbs to the HLA-Ia is inhibited dosimetrically by the adjacent peptides, (115)QFAYDGKDY(123) and (137)DTAAQI(142), but not by (126)LNEDLRSWTA(135), another closer shared peptide sequence. The inhibitory peptide sequences in HLA-E are at the alpha2-helix terminal facing beta(2)m. The HLA-Ia alleles recognized by HLA-E-MAb (e.g., MEM-E/02) are similar to those recognized by the natural anti-HLA antibodies found in the sera of healthy non-alloimmunized males. This study postulates that some, if not all, of the natural HLA-Ia antibodies seen in healthy males could be anti-HLA-E antibodies cross-reacting with HLA-Ia alleles.

Lack of an association between hydatid disease and autoimmunity

The prolonged survival of Echinococcus granulosus within the human host indicates that some mechanism is operating to permit parasite evasion of the host immune response. Several publications have described autoimmune phenomena in patients infected with hydatid cysts. The aim of this study was to test the postulate that there is a higher prevalence of autoantibodies in serum from patients with hydatid disease than in control samples, and this may provide some evidence of an association between autoimmunity and E. granulosus infection. Sera from 70 patients with hydatid disease and 45 control subjects were assayed for the presence of antinuclear antibodies (ANA), tissue specific autoantibodies and rheumatoid factor. All patients were aged between 20 and 80 years of age with no known history of autoimmune disease. Hydatid patients were surgically confirmed cases. Control subjects were chosen on the basis that they were age and sex matched to the test sera and had no known illness at the time blood samples were obtained. On the basis of an ANA autoantibody titre of > 1:40 being regarded as positive, 19 (27%) of the hydatid patients, 13 (28%) of the controls were positive. Low levels of tissue specific autoantibodies and rheumatoid factor were detected in sera from 5 (7%) and 2 (11%) hydatid patients and 4 (8%) and 3 (16%) of control subjects respectively. No significant differences (P > 0.05) were found between autoantibody levels in the hydatid patient sera and the controls. These findings suggest that there is no association between hydatid infection and the level of autoantibodies to a broad range of self antigens.

Limiting dilution analysis of autoreactive T cells in patients affected by hydatid disease

We evaluated the peripheral autoreactive response in patients with Echinococcus granulosus compared with healthy individuals. A limiting dilution analysis (LDA) was performed to estimate frequency of auto-reactive T cells and to detect the complex mechanism that often underlies the autoreactive response. Different LDA curves were seen in healthy controls and patients. The control group provided a straight line passing through the origin ('single hit' kinetics), indicating that only peripheral autoreactive T cells are limiting. On the other hand, autoreactive T cell titration in hydatid patients did not follow 'single hit' kinetics, suggesting that two or more cell types are titrated. More interestingly, we observed a very high frequency of autoreactive T cells in hydatid patients (1/1,000 to 1/2,500) compared with healthy controls (1/5,000 to 1/35,000). These data suggest that chronic infection may provide adequate stimuli for the induction of autoimmune disorders and increase in autoreactive T cells.

Molecular and immunological diagnosis of echinococcosis

Echinococcosis is an infectious disease of humans caused by the larval (metacestode) stage of the cestode species Echinococcus granulosus (cystic echinococcosis or hydatid disease) or Echinococcus multilocularis (alveolar echinococcosis or alveolar hydatid disease). Clinical manifestations depend primarily on localization and size of hepatic lesions and may include hepatomegaly, obstructive jaundice, or cholangitis. Prognostically, alveolar echinococcosis is considered similar to liver malignancies, including a lethality rate of 90% for untreated cases. Diagnosis is based on imaging techniques coupled with immunodiagnostic procedures. Antibody detection tests for E. multilocularis have markedly improved with the use of affinity-purified Em2 antigen and recombinant antigen II/3-10 in enzyme immunoassays. Antigens of corresponding quality for E. granulosus are still unavailable. The detection of circulating antigens and immune complexes in the sera of patients with cystic echinococcosis, the demonstration of in vitro lymphocyte proliferation in response to stimulation with Echinococcus antigens, and the discrimination of serum immunoglobulin isotype activity to various Echinococcus antigens in both cystic and alveolar echinococcosis have been suggested for diagnostic purposes as well as for monitoring patients after treatment. New diagnostic molecular tools include DNA probes for Southern hybridization tests and polymerase chain reaction for the amplification of E. multilocularis and E. granulosus species-specific DNA fragments.

Immunology and molecular biology of Echinococcus infections

Echinococcus spp. are the etiological agents of hydatid disease in man and other intermediate hosts. Many questions regarding the factors which determine susceptibility/resistance to hydatid disease, and the factors which influence the viability and fertility of hydatid cysts, remain to be answered. Recent research into the effects of hydatid infection on the immune system of the host has provided some insights into the host-parasite relationships. Immunochemical and recombinant DNA techniques are being applied to improve diagnosis of hydatidosis in man and E. granulosus infection in dogs, and also in the development of vaccines against infection with taeniid cestode larvae. The successes which have been achieved in these areas are likely to provide valuable tools for the control of cystic hydatidosis in man. These recent studies in the areas of immunobiology, serological diagnosis and vaccination are reviewed.