Immunochemical characterization of anti-albumin antibodies in liver diseases

Immune Dysfunction and Albumin-Related Immunity in Liver Cirrhosis

Liver cirrhosis yearly causes 1.2 million deaths worldwide, ranking as the 10th leading cause of death in the most developed countries. High susceptibility to infections along with a significant risk for infection-related mortality justifies the description of liver cirrhosis as the world's most common immunodeficiency syndrome. Liver cirrhosis is an end-stage organic disease hallmarked by a multifaceted immune dysfunction due to deterioration of antimicrobial recognition and elimination mechanisms in macrophages along with an impaired antigen presentation ability in circulating monocytes. Bacterial translocation supports—and is supported by—uncontrolled activation of immune cell responses and/or loss of toll-like receptor (TLR) tolerance, which can turn exaggerated inflammatory responses to systemic inflammation. Lipopolysaccharide (LPS) or endotoxin boosts systemic inflammatory activity through activation of TLR-2- and TLR-4-dependent pathways and facilitate a massive production of cytokines. This, in turn, results into elevated secretion of reactive oxygen species (ROS), which further enhances intestinal hyperpermeability and thus sustains a vicious circle of events widely known as “leaky gut.” Albumin can be of particular benefit in cirrhotic patients with spontaneous bacterial peritonitis and/or hepatorenal syndrome type of acute kidney injury (HRS-AKI) due to anti-inflammatory and antioxidative stress as well as volume-expanding properties and endothelial-stabilizing attributes. However, presence of autoantibodies against albumin in patients with liver cirrhosis has been described. Although previous research suggested that these antibodies should be regarded as naturally occurring antibodies (NOA), the origin of the antialbumin immune response is obscure. High occurrence of NAO/albumin complexes in patients with liver disease might reflect a limited clearance capacity due to bypassing portal circulation. Moreover, high burden of oxidized albumin is associated with less favorable outcome in patients with liver cirrhosis. To date, there is no data available as to whether oxidized forms of albumin result in neoepitopes recognized by the immune system. Nevertheless, it is reasonable to hypothesize that these alterations may have the potential to induce antialbumin immune responses and thus favor systemic inflammation.

Autoantibodies Against Albumin in Patients With Systemic Lupus Erythematosus

Objectives: Autoantibodies and aberrant immune complexes are pathological hallmarks of systemic lupus erythematosus (SLE). This study aimed to determine the occurrence of IgG autoantibodies against human serum albumin (anti-HSA IgG) and their potential association with antibodies against bovine serum albumin (anti-BSA IgG) in patients with SLE.

Methods: Sera of 180 SLE patients included to the Swiss SLE Cohort Study and 188 age- and sex-matched healthy controls were evaluated. Levels of anti-HSA IgG and anti-BSA IgG were quantified by ELISA. Selected samples were further characterized using serum fractions obtained by fast liquid chromatography (FPLC).

Results: SLE patients had increased levels of anti-HSA IgG (p = 0.002) but similar levels of anti-BSA IgG compared to matched healthy controls. Anti-HSA IgG levels correlated with the SLE Disease Activity Index (SLEDAI), which was more pronounced in patients with an physician's global assessment (PGA) of ≥ 1 (r = 0.309, p = 0.0066). Anti-HSA IgG was partially complexed with serum albumin but also occurred as monomeric autoantibodies in highly positive SLE patients. A positive correlation between anti-HSA IgG and anti-BSA IgG was found that was stronger in SLE patients than in healthy controls (r = 0.3172, p < 0.001 vs. r = 0.2122, p < 0.0035). Binding of anti-BSA IgG was inhibited partially in the presence of HSA in samples with double positivity for anti-HSA and anti-BSA (median inhibition 47.9%, range 0.9–100%) and vice versa.

Conclusion: In SLE patients there is an increased prevalence of anti-HSA IgG antibodies that are associated with SLE disease activity.

Immunoglobulin (Ig)G purified from human sera mirrors intravenous Ig human leucocyte antigen (HLA) reactivity and recognizes one's own HLA types, but may be masked by Fab complementarity-determining region peptide in the native sera

Intravenous immunoglobulin (IVIg) reacted with a wide array of human leucocyte antigen (HLA) alleles, in contrast to normal sera, due possibly to the purification of IgG from the pooled plasma. The reactivity of IgG purified from normal sera was compared with that of native sera to determine whether any serum factors mask the HLA reactivity of anti-HLA IgG and whether IgG purified from sera can recognize the HLA types of the corresponding donors. The purified IgG, unlike native sera, mirrored IVIg reactivity to a wide array of HLA-I/-II alleles, indicating that anti-HLA IgG may be masked in normal sera - either by peptides derived from soluble HLA or by those from antibodies. A < 3 kDa peptide from the complementarity-determining region (CDR) of the Fab region of IgG (but not the HLA peptides) masked HLA recognition by the purified IgG. Most importantly, some of the anti-HLA IgG purified from normal sera - and serum IgG from a few donors - indeed recognized the HLA types of the corresponding donors, confirming the presence of auto-HLA antibodies. Comparison of HLA types with the profile of HLA antibodies showed auto-HLA IgG to the donors' HLA antigens in this order of frequency: DPA (80%), DQA (71%), DRB345 (67%), DQB (57%), Cw (50%), DBP (43%), DRB1 (21%), A (14%) and B (7%). The auto-HLA antibodies, when unmasked in vivo, may perform immunoregulatory functions similar to those of therapeutic preparations of IVIg.

Elimination of circulatory IgM anti-HSA precedes anti-HBe seroconversion in patients with CAH type B

The presence of IgM and IgA antibodies with specificity for human serum albumin (HSA) were consecutively analyzed in serum samples from four patients with biopsy verified CAH type B during seroconversion in the HBe/anti-HBe antigen system. Circulatory IgM anti-HSA antibodies were present during HBe antigenemia. The antibody titers fluctuated, decreased, and were finally lost from the circulation. After the disappearance of IgM anti-HSA antibodies, seroconversion to anti-HBe reactivity occurred and a quiescent phase of the disease was established, as judged by normalization of transaminases and absence of circulatory HBV-DNA. IgA anti-HSA antibodies persisted in the circulation after the elimination of IgM anti-HSA and seroconversion to anti-HBe reactivity. For one of the patients, a dramatic increase in titers was followed by elimination of IgA anti-HSA and seroconversion to anti-HBs. The data indicate that the host "self"-component HSA, when associated with "foreign" HBe or HBs antigenic structures, elicit immune responses to HSA, preventing the adequate development of anti-HBe and anti-HBs. The cessation of anti-HSA reactivity, however, seemed to permit subsequent sensitization to HBe and HBs antigenic determinants, as detected by the presence of circulatory antibodies.

Interaction between rabbit IgG immune complexes and Ricinus agglutinin

Ricinus communis agglutinin covalently bound to Sepharose 4B (RcA-Sepharose 4B) was able to selectively bind immune complexes consisting of antigen (bovine serum albumin) and rabbit IgG antibody which were rich in antibody (i.e., high molecular weight complexes of approximately 2000 000). No interaction was recorded between RcA-Sepharose 4B and immune complexes consisting of the antigen plus rabbit IgG antibody which were rich in antigen (i.e., complexes with a molecular weight of 300 000-500 000). These results indicate that binding to RcA is due to the increased density of galactose residues in the high molecular weight polymeric antibody component of the soluble immune complexes.

Radioimmunoassay of IgG and IgM anti-albumin autoantibodies in human serum

An antigen-coated plate radioimmunoassay used to detect autoantibodies of IgG and IgM classes against human serum albumin is described. It comprises 3 steps: (a) adsorption of glutaraldehyde-polymerized human serum albumin on the wells of a plastic plate, (b) incubation of the serum to be tested with the antigen in the wells, and (c) the addition of radiolabelled antibodies against human IgG or IgM. The method has been used to estimate the level of anti-albumin autoantibodies (AAA) belonging to IgG or IgM classes in the sera of normal subjects and patients with liver diseases.

Reactivity of sera from patients with liver disease with glutaraldehyde-treated erythrocytes: role for false positive results in hemagglutination tests

The use of glutaraldehyde as a coupling reagent in the passive hemagglutination test (HA) has gained wide application, especially for the coating of red blood cells (RBC) with glutaraldehyde-polymerized human serum albumin (pHSA), for studies of the albumin receptor on hepatitis B surface antigen (HBsAg) or for the detection of anti-albumin antibodies (AAA). Here we report a previously unrecognized reactivity with glutaraldehyde-treated RBC mainly with sera from patients with liver disease. The highest incidences of this reaction were found in patients with acute viral hepatitis A and B, namely 44 of 50 (88%) and 31 of 50 (62%) respectively. In 234 HBsAg carriers the frequency was low (3%). This reactivity was also observed in 19 of 50 sera from patients with chronic liver disease documented by biopsy, but not in sera from 68 healthy subjects. By immunofluorescence on glutaraldehyde-treated RBC it was shown that the corresponding antibodies belonged mainly to the IgM class. In all HBsAg-negative patients studied the HA titer against glutaraldehyde-treated RBC was in agreement with the titer against RBC coated with pHSA or pBSA (polymerized bovine serum albumin). Absorption with pHSA abolished the reaction with glutaraldehyde-treated RBC in 7 of 8 sera, suggesting a common reactivity between glutaraldehyde-polymerized HSA and glutaraldehyde-treated RBC. Apart from the possible clinical importance of these antibodies, their existence is a possible source of false positive results when glutaraldehyde is used as a coupling reagent for immunological assays, in particular with sera from patients with liver diseases.