Immunoblotting techniques for the detection of low level homogeneous immunoglobulin components in serum

Isoelectric focusing followed by affinity immunoblotting to detect monoclonal free light chains in monoclonal gammopathies: Comparison with immunofixation electrophoresis and free light chain ratio

BACKGROUND

Isoelectric focusing (IEF) is a method with an exquisite resolution, and coupled with affinity immunoblotting (AIB), it can provide superior sensitivity to detect monoclonal free light chains (FLC).

METHODS

We tested the hypothesis that IEF/AIB is more sensitive and specific for monoclonal FLC detection in serum and urine samples than conventional methods, that is, electrophoresis (ELP), immunofixation (IF) and serum FLC ratio assessment. Investigation included 107 samples of 68 patients, among which 21 multiple myeloma patients were recently tested for minimal residual disease and 18 patients with AL amyloidosis.

RESULTS

Monoclonal FLC were detected by IEF/AIB in 37% of serum samples negative for monoclonal FLC on ELP/IF. As for urine samples, significant advantage of the IEF/AIB over ELP/IF was not demonstrated. Considering both serum and urine results, IEF/AIB definitely revealed monoclonal FLC in 20/83 (24%) of ELP/IF-negative samples. FLC ratio was abnormally high (>1.65) in all 11 patients definitely positive for monoclonal FLC kappa by IEF/AIB but also in 16/47 (34%) IEF/AIB-negative samples. Abnormally low values (<0.26) were found only in 10/28 samples (36%) positive for monoclonal FLC lambda. Appropriate use of renal FLC ratio reference range reduced the number of presumably false positives (6/47, i.e. 13%) but not false negatives (17/28, i.e. 61%).

CONCLUSIONS

The IEF/AIB method is more sensitive than IF and might be used in patients with negative IF results before deciding whether to proceed to minimal residual disease testing.

Comparison of Monoclonal Gammopathies Linked to Poliovirus or Coxsackievirus vs. Other Infectious Pathogens

Chronic stimulation by infectious pathogens or self-antigen glucosylsphingosine (GlcSph) can lead to monoclonal gammopathy of undetermined significance (MGUS) and multiple myeloma (MM). Novel assays such as the multiplex infectious antigen microarray (MIAA) and GlcSph assays, permit identification of targets for >60% purified monoclonal immunoglobulins (Igs). Searching for additional targets, we selected 28 purified monoclonal Igs whose antigen was not represented on the MIAA and GlcSph assays; their specificity of recognition was then analyzed using microarrays consisting of 3760 B-cell epitopes from 196 pathogens. The peptide sequences PALTAVETG and PALTAAETG of the VP1 coat proteins of human poliovirus 1/3 and coxsackievirus B1/B3, respectively, were specifically recognized by 6/28 monoclonal Igs. Re-analysis of patient cohorts showed that purified monoclonal Igs from 10/155 MGUS/SM (6.5%) and 3/147 MM (2.0%) bound to the PALTAVETG or PALTAAETG epitopes. Altogether, PALTAV/AETG-initiated MGUS are not rare and few seem to evolve toward myeloma.

Anti-Glucosylsphingosine Autoimmunity, JAK2V617F-Dependent Interleukin-1β and JAK2V617F-Independent Cytokines in Myeloproliferative Neoplasms

Simple Summary

Inflammation plays a major role in myeloproliferative neoplasms (MPNs) as regulator of malignant cell growth and mediator of clinical symptoms. Yet chronic inflammation may also be an early event that facilitates the development of MPNs. Here we analysed 42 inflammatory cytokines and report that in patients as well as in UT-7 cell lines, interleukin-1β and interferon-induced protein 10 (IP-10) were the main inflammatory molecules found to be induced by JAK2V617F, the most frequent driving mutation in MPNs. All other inflammatory cytokines were not linked to JAK2V617F, which implies that inflammation likely precedes MPN development at least in subsets of MPN patients. Consistently, a possible cause of early, chronic inflammation may be auto-immunity against glucolipids: we report that 20% of MPN patients presented with anti-glucosylsphingoside auto-antibodies. Since existing treatments can reduce glucosylsphingoside, this lysosphingolipid could become a new therapeutic target for subsets of MPN patients, in addition to JAK2V617F and inflammation.

Abstract

Inflammatory cytokines play a major role in myeloproliferative neoplasms (MPNs) as regulators of the MPN clone and as mediators of clinical symptoms and complications. Firstly, we investigated the effect of JAK2V617F on 42 molecules linked to inflammation. For JAK2V617F-mutated patients, the JAK2V617F allele burden (%JAK2V617F) correlated with the levels of IL-1β, IL-1Rα, IP-10 and leptin in polycythemia vera (PV), and with IL-33 in ET; for all other molecules, no correlation was found. Cytokine production was also studied in the human megakaryocytic cell line UT-7. Wild-type UT-7 cells secreted 27/42 cytokines measured. UT-7 clones expressing 50% or 75% JAK2V617F were generated, in which the production of IL-1β, IP-10 and RANTES was increased; other cytokines were not affected. Secondly, we searched for causes of chronic inflammation in MPNs other than driver mutations. Since antigen-driven selection is increasingly implicated in the pathogenesis of blood malignancies, we investigated whether proinflammatory glucosylsphingosine (GlcSph) may play a role in MPNs. We report that 20% (15/75) of MPN patients presented with anti-GlcSph IgGs, distinguished by elevated levels of 11 cytokines. In summary, only IL-1β and IP-10 were linked to JAK2V617F both in patients and in UT-7 cells; other inflammation-linked cytokines in excess in MPNs were not. For subsets of MPN patients, a possible cause of inflammation may be auto-immunity against glucolipids.

Analysis of the Targets and Glycosylation of Monoclonal IgAs From MGUS and Myeloma Patients

Previous studies showed that monoclonal immunoglobulins G (IgGs) of “monoclonal gammopathy of undetermined significance” (MGUS) and myeloma were hyposialylated, thus presumably pro-inflammatory, and for about half of patients, the target of the monoclonal IgG was either a virus—Epstein–Barr virus (EBV), other herpes viruses, hepatitis C virus (HCV)—or a glucolipid, lysoglucosylceramide (LGL1), suggesting antigen-driven disease in these patients. In the present study, we show that monoclonal IgAs share these characteristics. We collected 35 sera of patients with a monoclonal IgA (6 MGUS, 29 myeloma), and we were able to purify 25 of the 35 monoclonal IgAs (6 MGUS, 19 myeloma). Monoclonal IgAs from MGUS and myeloma patients were significantly less sialylated than IgAs from healthy volunteers. When purified monoclonal IgAs were tested against infectious pathogens and LGL1, five myeloma patients had a monoclonal IgA that specifically recognized viral proteins: the core protein of HCV in one case, EBV nuclear antigen 1 (EBNA-1) in four cases (21.1% of IgA myeloma). Monoclonal IgAs from three myeloma patients reacted against LGL1. In summary, monoclonal IgAs are hyposialylated and as described for IgG myeloma, significant subsets (8/19, or 42%) of patients with IgA myeloma may have viral or self (LGL1) antigen-driven disease.

Characteristics of MGUS and Multiple Myeloma According to the Target of Monoclonal Immunoglobulins, Glucosylsphingosine, or Epstein-Barr Virus EBNA-1

Chronic stimulation by infectious or self-antigens initiates subsets of monoclonal gammopathies of undetermined significance (MGUS), smoldering multiple myeloma (SMM), or multiple myeloma (MM). Recently, glucosylsphingosine (GlcSph) was reported to be the target of one third of monoclonal immunoglobulins (Igs). In this study of 233 patients (137 MGUS, 6 SMM, 90 MM), we analyzed the GlcSph-reactivity of monoclonal Igs and non-clonal Igs. The presence of GlcSph-reactive Igs in serum was unexpectedly frequent, detected for 103/233 (44.2%) patients. However, GlcSph was targeted by the patient’s monoclonal Ig for only 37 patients (15.9%); for other patients (44 MGUS, 22 MM), the GlcSph-reactive Igs were non-clonal. Then, the characteristics of patients were examined: compared to MM with an Epstein-Barr virus EBNA-1-reactive monoclonal Ig, MM patients with a GlcSph-reactive monoclonal Ig had a mild presentation. The inflammation profiles of patients were similar except for moderately elevated levels of 4 cytokines for patients with GlcSph-reactive Igs. In summary, our study highlights the importance of analyzing clonal Igs separately from non-clonal Igs and shows that, if autoimmune responses to GlcSph are frequent in MGUS/SMM and MM, GlcSph presumably represents the initial pathogenic event for ~16% cases. Importantly, GlcSph-initiated MM appears to be a mild form of MM disease.

Chemiluminescent detection of oligoclonal immunoglobulins after isoelectric focusing and affinity-mediated immunoblotting

BACKGROUND AND AIMS

Detection of oligoclonal IgG (o-IgG) in the cerebrospinal fluid (CSF) not found in serum is the principal laboratory test to support a diagnosis of multiple sclerosis. The aim of this study was to compare chemiluminescent and chromogenic detection of oligoclonal immunoglobulins in the cerebrospinal fluid and serum after their separation by means of isoelectric focusing followed by immunoblotting.

METHODS

A set of experiments was designed to detect oligoclonal immunoglobulins by means of alkaline phosphatase BCIP/NBT substrate and chemiluminescent peroxidase substrate.

RESULTS

Based on visual evaluation of signals, chemiluminescent detection requires about a 4 times lower amount of applied protein than very sensitive BCIP/NBT chromogenic detection. Very good correlation between methods has been shown for oligoclonal IgG. Antigen-specific oligoclonal IgG could be demonstrated by both methods although the pattern was clearer using chemiluminescence. In one patient, oligoclonal IgD bands barely visible by BCIP/NBT were convincingly demonstrated by chemiluminescence.

CONCLUSION

Chemiluminescent detection is a feasible option for oligoclonal immunoglobulin detection and could be used in cases when the sensitivity needs to be improved. Further studies and method optimisation are warranted.

Clonal Immunoglobulin against Lysolipids in the Origin of Myeloma

Antigen-driven selection has been implicated in the pathogenesis of monoclonal gammopathies. Patients with Gaucher's disease have an increased risk of monoclonal gammopathies. Here we show that the clonal immunoglobulin in patients with Gaucher's disease and in mouse models of Gaucher's disease-associated gammopathy is reactive against lyso-glucosylceramide (LGL1), which is markedly elevated in these patients and mice. Clonal immunoglobulin in 33% of sporadic human monoclonal gammopathies is also specific for the lysolipids LGL1 and lysophosphatidylcholine (LPC). Substrate reduction ameliorates Gaucher's disease-associated gammopathy in mice. Thus, long-term immune activation by lysolipids may underlie both Gaucher's disease-associated gammopathies and some sporadic monoclonal gammopathies.

Accurate identification of paraprotein antigen targets by epitope reconstruction

We describe the first successful clinical application of a new discovery technology, epitope-mediated antigen prediction (E-MAP), to the investigation of multiple myeloma. Until now, there has been no reliable, systematic method to identify the cognate antigens of paraproteins. E-MAP is a variation of previous efforts to reconstruct the epitopes of paraproteins, with the significant difference that it provides enough epitope sequence data so as to enable successful protein database searches. We first reconstruct the paraprotein's epitope by analyzing the peptides that strongly bind. Then, we compile the data and interrogate the nonredundant protein database, searching for a close match. As a clinical proof-of-concept, we apply this technology to uncovering the protein targets of para-proteins in multiple myeloma (MM). E-MAP analysis of 2 MM paraproteins identified human cytomegalovirus (HCMV) as a target in both. E-MAP sequence analysis determined that one para-protein binds to the AD-2S1 epitope of HCMV glycoprotein B. The other binds to the amino terminus of the HCMV UL-48 gene product. We confirmed these predictions using immunoassays and immunoblot analyses. E-MAP represents a new investigative tool for analyzing the role of chronic antigenic stimulation in B-lymphoproliferative disorders.

Monoclonal gammopathies in aging mu, kappa-transgenic mice: involvement of the B-1 cell lineage

Monoclonal gammopathies (MG) are monoclonal proliferative disorders of B cells at the differentiation stage of Ig production. They can be detected in the serum, either as transient or as persistent homogenous immunoglobulin (H-Ig) components. The exact phenotype, localization, and cell lineage origin of the precursor cells of MG are unknown, but may be crucial for both the correct diagnosis and for timely efficient treatment of the malignant forms. We used for the first time transgenic (Tg) mice (Sp6; mu/kappa) to study the origin of MG. In the mu, kappa Tg mice a small proportion of B cells can still produce endogenous IgM. These cells are of B-1 cell origin. The MG in Tg mice showed a later onset and a lower frequency than those in littermate control mice, mainly due to a four times lower frequency of benign monoclonal gammopathy. The 10% of B-1 cells that were able to produce endogenous Ig led to the development of MG in a frequency that was half the number of MG found in normal littermates. None of the MG in Tg mice produced an Ig of the Tg origin and therefore it can be concluded that they originated from B-1 cells.

Frequency of clonal dominance in the specific antibody response to DNP-HSA in CBA and C57BL mice reflects their susceptibility to age-associated development of monoclonal gammopathies

The effects of age, genetic background, and neonatal thymectomy on the levels and the heterogeneity of the specific antibody response were investigated in an experimental mouse model. Both intact and neonatally thymectomized (NTx) C57BL/KaLwRij (C57BL) and CBA/BrARij (CBA) mice were immunized at the age of 3 ("young") or 22 months ("old"). Highly sensitive antigen-specific immunoblotting techniques (ABL), in combination with agar-electrophoresis and isoelectric focusing (IEF), were used to investigate total specific antibody levels, the number of responding antigen-specific clonotypes, and the dominance of responding B cell clones in the antibody response against dinitrophenylated human serum albumin. After immunization, the specific antibody levels progressively increased in all experimental groups with the exception of old C57BL mice. All mice responded with a specific polyclonal heterogeneous response. In addition, some mice showed a clonal dominance of antibody-producing cells, as is reflected in the appearance of distinct homogeneous antibody components (H-Ab) in the sera. This clonal dominance was scarce in CBA mice but frequent in C57BL mice. Age at time of immunization and NTx had little if any additive effect on the incidence of H-Ab in either mouse strain. All dominant clones showed different electrophoretic mobility, indicating the proliferation of various clonotypes and not a strain-specific dominance of one clone. In old C57BL mice the specific antibody response was more restricted in heterogeneity, as is illustrated by more visible spectrotype bands in IEF and subsequent ABL. Hence, in old C57BL mice smaller amounts of specific antibodies were produced by fewer clones. Still, the incidence of H-Ab in this group was the same as that in the group of young C57BL mice. This indicates that at old age the responding B cell clones are more prone to becoming clonally dominant in C57BL mice. This tendency correlates with the high incidence of spontaneously developing monoclonal gammopathies in aging C57BL mice.

The SCID mouse as a model for multiple myeloma

The SCID mouse was investigated as a potential animal model for human multiple myeloma (MM). Duplicate samples of bone marrow mononuclear cells (BMMC) and/or peripheral blood mononuclear cells (PBMC) of six MM patients in different clinical phases and one patient with monoclonal gammapathy of undetermined significance (MGUS) were injected intraperitoneally into SCID mice. Human immunoglobulins (Ig) in the SCID sera were quantified with a light-chain isotype-specific ELISA, and their monoclonality biochemically characterized, using a sensitive immunoblotting technique after agar gel electrophoresis. Successful transplantation of bone marrow derived-tumour cells in SCID mice was obtained with BMCC of two MM patients with progressive disease. Human plasma cells were detected in the mesenteric fat tissue around the pancreas and the spleen. This model in SCID mice may facilitate studies on processes involved in tumour progression and provides a new tool for therapeutic approaches in MM.

Evidence for selective pressure in the appearance of monoclonal immunoglobulins during aging: studies in M54 mu-transgenic mice

Serum monoclonal immunoglobulins (M-Ig) appear during aging but little is known about the immunological factors which lead to their development. We have investigated whether such M-Ig occur as a clonally random process or result from V-region-directed selective pressures. We have analyzed a mu-transgenic mouse strain in which over 95% of all splenic B cells express the transgenic mu chain. All endogenous repertoire and mu-chain diversity are generated from the 5% of the B cells which express endogenous mu chains. Not one of the M-Ig detected in these mice were of transgene origin alone; 11 of the 14 M-Ig did not express a mu chain and none of the mu chain containing M-Ig expressed the transgene allotype alone. This observation suggests that the B cells giving rise to M-Ig are heavily selected from among the small number of B cells which express endogenous Ig. The selective factors that might act on the endogenous B cell pools are discussed.

Development of aging-associated monoclonal gammapathies with antibody activity to the antigen used for immunization of young mice

The influence of immunization with dinitrophenylated human serum albumin (DNP-HSA) at a young age on the development of age-related monoclonal gammapathies (MG) was investigated in a longitudinal study in intact and neonatally thymectomized (NTx) C57BL/KaLwRij and CBA/BrARij mice. Three-month-old mice were immunized four times in monthly intervals with DNP-HSA. Control mice received saline and adjuvant only. Mice immunized with DNP-HSA responded with heterogeneous antibodies, occasionally with some clonal dominance. The antibody levels further declined and were hardly detectable when the mice were 21 months old. Eighteen of 87 experimental mice developed homogeneous antibody components (H-Ab) to DNP-HSA with aging. Their frequencies per individual groups were 5, 22, 24, and 29% for intact CBA, NTx-CBA, NTx-C57BL, and intact C57BL mice, respectively. Some H-Ab had the same mobility and similar spectrotypes as dominant clonal products at the peak of the response. However, the majority of H-Ab appearing at old age were "new" H-Ab. While most of H-Ab in the CBA mice were transient and of a low concentration, the majority of H-Ab in the C57BL mice had all characteristics of a benign monoclonal gammapathy. The results indicate that memory cells of the B cell clones involved in the original specific response may in a susceptible strain become targets for events leading to the development of benign monoclonal gammapathy.