METABOLISM OF HUMAN GAMMA MACROGLOBULINS

Understanding the biosynthesis of human IgM SAM-6 through a combinatorial expression of mutant subunits that affect product assembly and secretion

Polymeric IgMs are secreted from plasma cells abundantly despite their structural complexity and intricate multimerization steps. To gain insights into IgM's assembly mechanics that underwrite such high-level secretion, we characterized the biosynthetic process of a natural human IgM, SAM-6, using a heterologous HEK293(6E) cell platform that allowed the production of IgMs both in hexameric and pentameric forms in a controlled fashion. By creating a series of mutant subunits that differentially disrupt secretion, folding, and specific inter-chain disulfide bond formation, we assessed their effects on various aspects of IgM biosynthesis in 57 different subunit chain combinations, both in hexameric and pentameric formats. The mutations caused a spectrum of changes in steady-state subcellular subunit distribution, ER-associated inclusion body formation, intracellular subunit detergent solubility, covalent assembly, secreted IgM product quality, and secretion output. Some mutations produced differential effects on product quality depending on whether the mutation was introduced to hexameric IgM or pentameric IgM. Through this systematic combinatorial approach, we consolidate diverse overlapping knowledge on IgM biosynthesis for both hexamers and pentamers, while unexpectedly revealing that the loss of certain inter-chain disulfide bonds, including the one between μHC and λLC, is tolerated in polymeric IgM assembly and secretion. The findings highlight the differential roles of underlying non-covalent protein-protein interactions in hexamers and pentamers when orchestrating the initial subunit interactions and maintaining the polymeric IgM product integrity during ER quality control steps, secretory pathway trafficking, and secretion.

Serum immunoglobulin and the threshold of Fc receptor-mediated immune activation

Antibodies can mediate immune recruitment or clearance of immune complexes through the interaction of their Fc domain with cellular Fc receptors. Clustering of antibodies is a key step in generating sufficient avidity for efficacious receptor recognition. However, Fc receptors may be saturated with prevailing, endogenous serum immunoglobulin and this raises the threshold by which cellular receptors can be productively engaged. Here, we review the factors controlling serum IgG levels in both healthy and disease states, and discuss how the presence of endogenous IgG is encoded into the functional activation thresholds for low- and high-affinity Fc receptors. We discuss the circumstances where antibody engineering can help overcome these physiological limitations of therapeutic antibodies. Finally, we discuss how the pharmacological control of Fc receptor saturation by endogenous IgG is emerging as a feasible mechanism for the enhancement of antibody therapeutics.

SARS-CoV-2 Seroprevalence and Antibody Kinetics Among Health Care Workers in a Spanish Hospital After 3 Months of Follow-up

Background

At the COVID-19 spring 2020 pandemic peak in Spain, prevalence of SARS-CoV-2 infection in a cohort of 578 randomly selected health care workers (HCWs) from Hospital Clínic de Barcelona was 11.2%.

Methods

A follow-up survey 1 month later (April-May 2020) measured infection by rRT-PCR and IgM, IgA, and IgG to the receptor-binding domain of the spike protein by Luminex. Antibody kinetics, including IgG subclasses, was assessed until month 3.

Results

At month 1, the prevalence of infection measured by rRT-PCR and serology was 14.9% (84/565) and seroprevalence 14.5% (82/565). We found 25 (5%) new infections in 501 participants without previous evidence of infection. IgM, IgG, and IgA levels declined in 3 months (antibody decay rates 0.15 [95% CI, .11–.19], 0.66 [95% CI, .54–.82], and 0.12 [95% CI, .09–.16], respectively), and 68.33% of HCWs had seroreverted for IgM, 3.08% for IgG, and 24.29% for IgA. The most frequent subclass responses were IgG1 (highest levels) and IgG2, followed by IgG3, and only IgA1 but no IgA2 was detected.

Conclusions

Continuous and improved surveillance of SARS-CoV-2 infections in HCWs remains critical, particularly in high-risk groups. The observed fast decay of IgA and IgM levels has implications for seroprevalence studies using these isotypes.

Structure, Function, and Therapeutic Use of IgM Antibodies

Natural immunoglobulin M (IgM) antibodies are pentameric or hexameric macro-immunoglobulins and have been highly conserved during evolution. IgMs are initially expressed during B cell ontogeny and are the first antibodies secreted following exposure to foreign antigens. The IgM multimer has either 10 (pentamer) or 12 (hexamer) antigen binding domains consisting of paired µ heavy chains with four constant domains, each with a single variable domain, paired with a corresponding light chain. Although the antigen binding affinities of natural IgM antibodies are typically lower than IgG, their polyvalency allows for high avidity binding and efficient engagement of complement to induce complement-dependent cell lysis. The high avidity of IgM antibodies renders them particularly efficient at binding antigens present at low levels, and non-protein antigens, for example, carbohydrates or lipids present on microbial surfaces. Pentameric IgM antibodies also contain a joining (J) chain that stabilizes the pentameric structure and enables binding to several receptors. One such receptor, the polymeric immunoglobulin receptor (pIgR), is responsible for transcytosis from the vasculature to the mucosal surfaces of the lung and gastrointestinal tract. Several naturally occurring IgM antibodies have been explored as therapeutics in clinical trials, and a new class of molecules, engineered IgM antibodies with enhanced binding and/or additional functional properties are being evaluated in humans. Here, we review the considerable progress that has been made regarding the understanding of biology, structure, function, manufacturing, and therapeutic potential of IgM antibodies since their discovery more than 80 years ago.

The B cell immunobiology that underlies CNS autoantibody-mediated diseases

A rapidly expanding and clinically distinct group of CNS diseases are caused by pathogenic autoantibodies that target neuroglial surface proteins. Despite immunotherapy, patients with these neuroglial surface autoantibody (NSAb)-mediated diseases often experience clinical relapse, high rates of long-term morbidity and adverse effects from the available medications. Fundamentally, the autoantigen-specific B cell lineage leads to production of the pathogenic autoantibodies. These autoantigen-specific B cells have been consistently identified in the circulation of patients with NSAb-mediated diseases, accompanied by high serum levels of autoantigen-specific antibodies. Early evidence suggests that these cells evade well-characterized B cell tolerance checkpoints. Nearer to the site of pathology, cerebrospinal fluid from patients with NSAb-mediated diseases contains high levels of autoantigen-specific B cells that are likely to account for the intrathecal synthesis of these autoantibodies. The characteristics of their immunoglobulin genes offer insights into the underlying immunobiology. In this Review, we summarize the emerging knowledge of B cells across the NSAb-mediated diseases. We review the evidence for the relative contributions of germinal centres and long-lived plasma cells as sources of autoantibodies, discuss data that indicate migration of B cells into the CNS and summarize insights into the underlying B cell pathogenesis that are provided by therapeutic effects.

Plasma therapy leads to an increase in functional IgA and IgM concentration in the blood and saliva of a patient with X-linked agammaglobulinemia

BACKGROUND

Patients with X-linked agammaglobulinemia (XLA) are protected against invasive bacterial infections due to IgG replacement therapy, but are still at higher risk for mucosal infections of the gut and respiratory tract. This might be explained by to the lack of IgA and IgM, as these antibodies are especially important for protection against invading bacterial pathogens on the mucosal surface.

METHODS

In an attempt to eliminate a chronic norovirus infection in a patient with X-linked agammaglobulinemia, fresh frozen plasma (FFP) was given two times a week for 3 weeks. At each visit, pre- and post-FFP infusion serum and saliva was collected to determine IgG-, IgA- and IgM-concentrations and serum half-life was calculated. Functionality of the immunoglobulins pre- and post-FFP infusion in both serum and saliva was tested by measuring complement activation, agglutination and killing of non-typeable Haemophilus influenzae (NTHi).

RESULTS

Administration of FFP failed to eradicate the chronic norovirus infection. Serum IgA and IgM half-life was 4.2 ± 0.3 and 3.8 ± 0.3 days, respectively. The presence of serum IgM was associated with increased complement binding and complement-mediated killing of NTHi. IgA in saliva was detectable post-FFP and was associated with increased agglutination of NTHi. IgM in saliva was not detectable.

CONCLUSIONS

We conclude that FFP treatment, although ineffective in clearing a chronic norovirus infection in this single patient, might be beneficial to prevent or eliminate bacterial infections in XLA patients by increasing IgM dependent complement-mediated killing in serum and IgA dependent bacterial agglutination on the mucosal surface.

Limited Innovations After More Than 65 Years of Immunoglobulin Replacement Therapy: Potential of IgA- and IgM-Enriched Formulations to Prevent Bacterial Respiratory Tract Infections

Patients with primary immunoglobulin deficiency have lower immunoglobulin levels or decreased immunoglobulin function, which makes these patients more susceptible to bacterial infection. Most prevalent are the selective IgA deficiencies (~1:3,000), followed by common variable immune deficiency (~1:25,000). Agammaglobulinemia is less common (~1:400,000) and is characterized by very low or no immunoglobulin production resulting in a more severe disease phenotype. Therapy for patients with agammaglobulinemia mainly relies on prophylactic antibiotics and the use of IgG replacement therapy, which successfully reduces the frequency of invasive bacterial infections. Currently used immunoglobulin preparations contain only IgG. As a result, concurrent IgA and IgM deficiency persist in a large proportion of agammaglobulinemia patients. Especially patients with IgM deficiency remain at risk for recurrent infections at mucosal surfaces, which includes the respiratory tract. IgA and IgM have multiple functions in the protection against bacterial infections at the mucosal surface. Because of their multimeric structure, both IgA and IgM are able to agglutinate bacteria efficiently. Agglutination allows for entrapment of bacteria in mucus that increases clearance from the respiratory tract. IgA is also important for blocking bacterial adhesion by interfering with bacterial adhesion receptors. IgM in its place is very well capable of activating complement, therefore, it is thought to be important in complement-mediated protection at the mucosal surface. The purpose of this Mini Review is to highlight the latest advances regarding IgA- and IgM-enriched immunoglobulin replacement therapy. We describe the different IgA- and IgM-enriched IgG formulations, their possible modes of action and potential to protect against respiratory tract infections in patients with primary immunoglobulin deficiencies.

Therapeutic plasma exchange: a technical and operational review

Therapeutic plasma exchange (TPE) is an extracorporeal blood purification technique designed for the removal of large molecular weight substances. Examples of these substances include pathogenic autoantibodies, immune complexes, cryoglobulins, myeloma light chains, endotoxin and cholesterol containing lipoproteins. The basic premise of the treatment is that removal of these substances will allow for the reversal of the pathologic processes related to their presence. This review will cover the techniques for performing TPE, the kinetics of the removal of large molecules from the plasma and the benefits and risks of the different types of replacement fluids.

A Temporal Model of Human IgE and IgG Antibody Function

The diversity of the human antibody repertoire that is generated by V(D)J gene rearrangement is extended by nine constant region genes that give antibodies their complex array of effector functions. The application of high throughput sequencing to the study of V(D)J gene rearrangements has led to significant recent advances in our understanding of the antigen-binding repertoire. In contrast, our understanding of antibody function has changed little, and mystery still surrounds the existence of four distinctive IgG subclasses. Recent observations from murine models and from human studies of VDJ somatic point mutations suggest that the timing of emergence of cells from the germinal center may vary as a consequence of class switching. This should lead to predictable differences in affinity between isotypes. These differences, and varying abilities of the isotypes to fix complement and bind FcRs, could help coordinate the humoral defenses over the time course of a response. We therefore propose a Temporal Model of human IgE and IgG function in which early emergence of IgE sensitizes sentinel mast cells while switching to IgG3 recruits FcγR-mediated functions to the early response. IgG1 then emerges as the major effector of antigen clearance, and subsequently IgG2 competes with IgG1 to produce immune complexes that slow the inflammatory drive. Persisting antigen may finally stimulate high affinity IgG4 that outcompetes other isotypes and can terminate IgG1/FcγR-mediated activation via the inhibitory FcγRIIB. In this way, IgG antibodies of different subclasses, at different concentrations and with sometimes opposing functions deliver cohesive, protective immune function.

Linking influenza virus tissue tropism to population-level reproductive fitness

Influenza virus tissue tropism defines the host cells and tissues that support viral replication and contributes to determining which regions of the respiratory tract are infected in humans. The location of influenza virus infection along the respiratory tract is a key determinant of virus pathogenicity and transmissibility, which are at the basis of influenza burdens in the human population. As the pathogenicity and transmissibility of influenza virus ultimately determine its reproductive fitness at the population level, strong selective pressures will shape influenza virus tissue tropisms that maximize fitness. At present, the relationships between influenza virus tissue tropism within hosts and reproductive fitness at the population level are poorly understood. The selective pressures and constraints that shape tissue tropism and thereby influence the location of influenza virus infection along the respiratory tract are not well characterized. We use mathematical models that link within-host infection dynamics in a spatially-structured human respiratory tract to between-host transmission dynamics, with the aim of characterizing the possible selective pressures on influenza virus tissue tropism. The results indicate that spatial heterogeneities in virus clearance, virus pathogenicity or both, resulting from the unique structure of the respiratory tract, may drive optimal receptor binding affinity--that maximizes influenza virus reproductive fitness at the population level--towards sialic acids with α2,6 linkage to galactose. The expanding cell pool deeper down the respiratory tract, in association with lower clearance rates, may result in optimal infectivity rates--that likewise maximize influenza virus reproductive fitness at the population level--to exhibit a decreasing trend towards deeper regions of the respiratory tract. Lastly, pre-existing immunity may drive influenza virus tissue tropism towards upper regions of the respiratory tract. The proposed framework provides a new template for the cross-scale study of influenza virus evolutionary and epidemiological dynamics in humans.

Immunoglobulin M as a vaccine adjuvant

Vaccines are effective in preventing disease by stimulating the immune system and sustaining an immune response towards eradication of pathogens and diseased cells. However, designing successful vaccines is not always straightforward. For a vaccine to be successful, antigen-presenting cells (APC) need to be stimulated, primarily by adjuvants, towards a sustained immune response through integration of the innate and adaptive (humoral and cellular) immune systems. Furthermore, there is an immediate need for safe and effective adjuvants. There has been significant progress in understanding the mechanisms on how vaccines work and the role of adjuvants, dendritic cells, and the toll-like receptor (TLR) pathway. Currently, different adjuvants are actively explored but the potential of the immunoglobulin M (IgM) as a vaccine adjuvant has been overlooked. This article hypothesizes how the IgM molecule could function as a vaccine adjuvant by acting as a "soluble" toll-like receptor (TLR) through the formation of an immune complex with antigen (Ag) and other components of the innate immune system. The complex should lead to sustained humoral and/or cell-mediated immune responses. Hypothetically, it is also possible that the Ag-IgM complex recruits other components of complement or other factors that can activate other members of the adaptive immune system. As it is now possible to produce commercial-scale quantities of monoclonal human IgM antibodies, understanding the role of the IgM in linking the innate and adaptive immune systems may lead to practical therapeutic applications.

Levels of autoantibodies, unlike antibodies to all extrinsic antigen groups, fall following B cell depletion with Rituximab

Many autoantibodies have variable-region sequences indicating their production in an affinity-matured antibody response involving germinal centers (GC). Plasma cells from GC can be long-lived, do not express CD20 and thus should not be depleted by a therapeutic monoclonal Ab against human CD20 - Rituximab. Nevertheless, autoantibody titers often fall following Rituximab treatment. To test if this reflects exclusive production by short-lived plasma cells in extrafollicular Ab responses, we monitored, after Rituximab treatment, levels of natural Ab and Ab against extrinsic antigens that do not induce productive GC. Eleven patients with active vasculitis and anti-proteinase-3 (PR3) Ab were assessed before and during 5 months after Rituximab therapy. Blood B cells were undetectable within 2 wk, and all patients achieved clinical remission. Levels of natural Ab - isohemagglutinins and anti-phosphorylcholine Ab - and Ab levels against thymus-independent and thymus-dependent extrinsic antigens were little affected. By contrast, 5 months after Rituximab, IgG autoantibody against PR3 had fallen to a median of 22% of pretreatment values. While the kinetics of this fall do not suggest an intrinsically short lifespan of autoantibody-producing cells, the data are consistent with Rituximab causing loss of sites within inflammatory tissues that selectively sustain autoantibody-producing cells.

National Survey of Hemapheresis Practice in Hungary 2001?2004

In the current study, the authors evaluated data provided by Hungarian hemapheresis centers to the National Health Insurance (NHI) organization between 2001 and 2004 with the intention of having costs reimbursed. The primary objective of the present study was to rank data by frequency of indications of therapeutic plasma exchange (TPE). Furthermore, we compared frequency data with the Canadian TPE Registry and reviewed medical evidence regarding the adequacy of applying TPE at chosen indications based on data in literature. It was concluded that the number of TPEs (and thus the reimbursed costs) increased steadily year by year. It is worth considering the difference between the five most frequent indications of TPE in Hungary or in Canada. Clinicians tend to apply TPE in many cases as a last resort treatment of many diseases unresponsive to conventional therapy. Consequently, there are many illnesses for which the value of TPE is still questionable (or unproven) and its use is considered investigational or experimental. Nevertheless, cumulative medical experience does not always confirm the adequacy of TPE in all treatments, retrospectively. Thus, limited financial resources oblige clinicians to be judicious in providing apheresis services.

THE IMMUNOGLOBULINS OF MICE. I. FOUR MAJOR CLASSES OF IMMUNOGLOBULINS: 7S GAMMA-2-, 7S GAMMA-1-, GAMMA-1A (BETA-2A)-, AND 18S GAMMA-1M-GLOBULINS

Two classes of 7S γ-globulins are identified in normal mouse serum and are designated 7S γ₂-globulins and 7S γ₁-globulins. These two immunoglobulin classes are similar in size. They differ in range of electrophoretic mobility, in specific antigenic determinants, and in genetically determined isoantigens. Four classes of immunoglobulins in mouse serum, i.e. 7S γ₂-, 7S γ₁-, γ_1A (β_2A), and γ_M-globulins, were shown to have antibody activity. Each class was characterized and shown to have distinctive immunochemical and physicochemical properties. The genetically determined isoantigens, Iga-1 and Iga-2, were shown to be present only on 7S γ₂-globulin molecules.

THE IMMUNOGLOBULINS OF MICE. V. THE METABOLIC (CATABOLIC) PROPERTIES OF FIVE IMMUNOGLOBULIN CLASSES

The metabolic properties of immunoglobulin were investigated by comparing five classes of mouse immunoglobulin. Three forms of 7S immunoglobulin had different rates of catabolism. The fractional rates of catabolism were found to be about 13 per cent per day for 7S γ_2a-globulin; 25 per cent for 7S γ_2b-globulin; and 17 per cent for 7S γ₁-globulin. Catabolism of the three classes of 7S γ-globulin (γ_2a, γ_2b, and γ₁) were prolonged at low serum 7S γ-globulin levels and accelerated at high serum 7S γ-globulin levels. Each of the 7S γ-globulin components was influenced by the serum level of the other mouse 7S γ-globulin components and by exogenously administered human 7S γ-globulin. They were not appreciably altered, however, by the serum level of IgA (γ₁A-, β₂A-globulin). The progressively changing (longer) half-times observed in turnover studies of normal IgG (7S γ-globulin) may be caused by catabolic heterogeneity of normal 7S immunoglobulins which are immunochemically and catabolically related to γ_2a-, γ_2b-, and 7S γ₁-myeloma proteins. These studies indicate that the 7S γ_2a-, 7S γ_2b-, and 7S γ₁-globulins share a common catabolic control mechanism. This mechanism is influenced by the serum level of each of these components, but is independent of the serum level of IgA (γ₁A-globulin) and probably is independent of IgM (γ₁M-globulin). Catabolism of IgA (γ₁A-, β₂A-globulin) and IgM (γ₁M-globulin) was much more rapid than the catabolism of the 7S γ-globulins. The halftimes of the IgA and IgM were approximately 1.2 and 0.5 days respectively. The fractional rate of catabolism of IgA and IgM seemed to be independent of their serum concentration. The rate of catabolism, as well as the rate of synthesis, was shown to play a major role in determining the serum level of each class of immunoglobulin.

Use of hu-IgG-SCID mice to evaluate the in vivo stability of human monoclonal IgG antibodies

Human and in vitro modified mAbs such as humanized rodent mAbs and immunotoxins are now considered for a variety of applications in humans. The adequate in vivo stability of these Ig preparations is not easily predicted from in vitro studies and may be essential for many therapeutic applications. In this study, we report the development and characterization of an in vivo model for testing this parameter using SCID mice containing a physiological concentration of human IgG (hu-IgG-SCID). The model was tested with several IgG1 and IgG3 human mAbs reacting with the human Rh(D) red cell antigen. It is known that human IgG have a shorter half-life in SCID mice than in humans. However, our results showed that the half-life of IgG3 mAbs (1.5 +/- 0.5 days) was much shorter than the one of IgG1 mAbs (5.8 +/- 1.4 days), indicating that the relative stability of IgG1 and IgG3 human mAbs in hu-IgG-SCID mice is similar to the one previously reported in humans (21 days vs. 7 days respectively). The IgG catabolism rate in humans is known to be inversely proportional to serum IgG concentrations. Accordingly, the dilution of the mAbs in a large excess (200-fold) of human IgG was found to be an important parameter of the hu-IgG-SCID mouse model since much longer (3-4-fold) mAb half-lives were obtained in the presence of a lower dose or in the absence of co-injected human IgG. This study show the usefulness of this animal model for the evaluation of human antibody stability in an in vivo environment.

Phase I study of antilipopolysaccharide human monoclonal antibody MAB-T88

Monoclonal antibody MAB-T88 is a human monoclonal immunoglobulin M antibody directed at the lipopolysaccharide of gram-negative bacteria. In this study, nine patients who were expected to become neutropenic from antineoplastic chemotherapy received an infusion of MAB-T88, three patients at each of three doses: 1, 4, and 8 mg/kg of body weight. MAB-T88 was shown to be safe, with an effective half-life in plasma of 25.4 h, and no patient developed immunoglobulin G antibody to MAB-T88.

Plasma exchange with a rotating filter

We have modified a rotating filter system to provide therapeutic plasma exchange. Seventeen patients underwent 188 treatments. Blood flows to the filter ranged from 75 to 100 ml/min; mean filtration fraction was 64 +/- 1% (+/- SE, N = 188). Mean plasma removal rate per treatment was 40.2 +/- 0.6 ml/min; net plasma removed per treatment was 3231 +/- 53 ml (N = 188); mean treatment time was 83 +/- 2 minutes (N = 188). Mean percent decline in platelet count was 15 +/- 4% (N = 46). Immunoglobulin kinetics were evaluated in order to validate our method of treatment prescription. The apparent volume of distribution (AVD) for each immunoglobulin class was compared to our estimate for plasma volume (EPV). The fraction AVD/EPV for IgG was 0.97 +/- 0.04 (N = 14), for IgA was 0.87 +/- 0.04 (N = 13) and for IgM was 0.96 +/- 0.3 (N = 26). Use of the EPV allowed for accurate prediction of treatment results. Correlation between expected and actual decline in serum levels revealed an r value of 0.86 for IgG (P = 0.0002), 0.88 for IgA (P = 0.0001), and 0.57 for IgM (P less than 0.003). We conclude that a rotating filter system can provide a highly efficient means of plasma exchange. The use of a simplified method of estimating plasma volume allows for a reliable prediction of treatment results.

Human IgM monoclonal antibody 16.88: pharmacokinetics and distribution in mouse and man

Human IgM monoclonal antibody (MAb) 16.88 recognizes an antigen strongly expressed by colon cancer tissue. We used 131I-labelled 16.88 for biodistribution and pharmacokinetic studies in nude mice bearing WiDr or NIH:OVCAR-3 xenografts. Serum half-life was 8 h. Maximum tumour uptake was between 1 and 8 h after administration and amounted to, respectively, 3% and 1% of the injected dose g-1 for WiDr and NIH:OVCAR-3 tumours. Half-lives in these tumours were approximately 24 h. Tumour to normal colon uptake ratios increased from 2.3 at 24 h to 17 at 5 days after injection. Simultaneously, pharmacokinetic studies were performed in patients with advanced colon cancer reactive with 16.88. They were injected with 5 mCi 131I-16.88 by intravenous infusion over 2 h. Serum half-life was 20 h with greater than 90% of the 131I bound to 16.88. Within 40 h 50% of the injected dose was excreted as free 131I in the urine. In one patient an accelerated clearance was found, possibly caused by pre-existing antibodies reacting with 16.88. None of the patients showed an immune response against 16.88 antibody. Immunoscintigraphy showed positive tumour localization in the majority of the patients, best visualized at later days. We conclude that 16.88 has tumour localization properties while its human origin accounts for the lack of immunogenicity.

Secretory component-binding properties of normal serum IgM

Our aim was to investigate why serum IgM is poorly transferred into secretions in normal subjects. Indeed, the low IgM level in secretions contrasts with the capacity of monoclonal IgM to bind to secretory component (SC), but it is not well established to what extent normal serum IgM can do so. The mean SC affinity was studied with a polyclonal IgM preparation from 250 normal subjects and with a representative pool of 100 different monoclonal IgM. The SC-binding percentages varied as a function of the IgM/SC molar ratio according to a common hyperbolic curve, with similar association constants: Ka = 4.19 +/- 2.61 x 10(7) M-1 (polyclonal pool) and Ka = 5.80 +/- 2.73 x 10(7) (monoclonal pool). It thus appears that the large difference in IgM concentrations between blood and secretions cannot be due to an SC-binding defect of serum IgM, but is probably explained by its low diffusion from blood to the extravascular compartment.

Immunologic and pharmacologic concepts of monoclonal antibodies

While monoclonal antibodies have solved many of the difficulties of using immunologic reagents for radioimmunodiagnosis and therapy, in the 13 years since their introduction a number of persistent problems remain, most notably a low yield of antibody-producing cells from the fusion process, difficulty in obtaining high-affinity antibodies, and the potential immunogenicity of murine immunoglobulins (Igs). Several solutions are under development, including fusion techniques that enrich for cells producing desired antibodies, production of human-mouse chimeric antibodies by recombinant DNA technology, and the generation of human monoclonal antibodies by promising new approaches. Until these upcoming methodologies are established, and to better direct their development and application, a sound understanding of the pharmacology of presently available native and modified monoclonal antibodies is crucial. Although much has been already determined in this area, a great deal of further clarification remains necessary.

Metabolism of immunoglobulin E in patients with markedly elevated serum immunoglobulin E levels

The metabolism of human IgE was studied in normals, severe atopics, and patients with the hyperimmunoglobulin E-recurrent infection (HIE; Job's) syndrome to determine whether IgE metabolism is altered in patients with marked elevation of serum IgE. Purified polyclonal 125I-IgE was administered intravenously and serial plasma and urine samples were obtained. After analysis, the metabolic data support previously published evidence that IgE (at concentrations found in normal individuals) is catabolized at a higher fractional rate than other immunoglobulins and is catabolized by both an intravascular and an extravascular pathway. In addition, the data show that the fractional catabolic rate for IgE is significantly less for the atopic patients (mean +/- SEM = 0.20 +/- 0.01) and for the HIE patients (0.15 +/- 0.02) than for the normal volunteers (0.52 +/- 0.06; P less than 0.01) and is inversely related (r = -0.851; P less than 0.001) to the serum IgE concentration. These findings have specific importance in showing that decreased fractional catabolic rate contributes substantially to elevation of IgE in atopic and HIE patients. In addition, the findings have general significance in that they lead to a unifying hypothesis of immunoglobulin catabolism.

Discriminant analysis of Hodgkin's disease and non-Hodgkin's lymphomas by age and serum proteins

Immunonephelometric evaluations of 13 serum proteins were made in 71 patients with two types of lymphoproliferative diseases: Hodgkin's disease (32 patients) and non-Hodgkin's lymphomas (39 patients). The subjects were differentiated by discriminant analysis by means of age and three selected proteins: properdin factor B, IgM and ceruloplasmin. The results obtained permitted classification of 90% of the cases reported.

PWM-induced generation of immunoglobulin-secreting cells in patients with multiple myeloma

The pokeweed-mitogen-induced transformation of B-lymphocytes into immunoglobulin-secreting cells was studied in vitro in 25 patients with multiple myeloma using a reverse hemolytic plaque assay. Fifteen patients showed a good response in generating immunoglobulin-secreting cells, whereas 10 patients showed a decreased B cell reactivity which was not due to intermittent melphalan/steroid therapy administered to 15 patients. Experiments with lymphocyte subpopulations demonstrated that the inability of some multiple-myeloma patients to generate immunoglobulin-secreting cells was always based on a defect in the B-cell subset. Co-culture experiments with lymphocytes from normal individuals and patients revealed a cell-mediated suppression in one case, whereas humoral suppressive factors in the patients' serum could not be observed using the reverse hemolytic plaque assay. Patients were classified into three groups: (a) patients with a normal B-cell function, (b) patients with a reversible, tumor-dependent suppression of B-cell reactivity and (c) patients in whom the normal B-cell population was replaced by non-reactive cells.

Inhibition of de novo IgM antibody synthesis by thalidomide as a relevant mechanism of action in leprosy

Thalidomide is well documented to be an effective treatment for erythema nodosum leprosum (ENL) occurring in lepromatous leprosy. To be beneficial, thalidomide must interfere with one or more of the several essential steps in the pathogenesis of this syndrome, which is presumed to be a clinical manifestation of an Arthur-type hypersensitivity. Since complexes of antigen and antibody would initiate these events, thalidomide could exert its most direct influence on reactants in this essential step. To determine whether thalidomide affected de novo antibody synthesis, the effect of the drug on the antibody response to sheep erythrocytes in mice was determined. Thalidomide significantly inhibited IgM antibody formation when fed to mice for 5 or 7 days before immunization with sheep erythrocytes. There was also a selective decrease in serum IgM concentrations among leprosy patients being treated with thalidomide for ENL. A clinically relevant site of action of thalidomide in ENL appears to be on the synthesis of IgM antibody. The target site of the drug among the macrophage, antibody-forming, and helper or suppressor lymphocytes remains to be elucidated.

The site of protein loss in Schönlein-Henoch purpura

Schönlein-Henoch purpura may be complicated by hypoproteinaemia, which in most patients is due to the development of nephrotic syndrome. However, in some proteinuria is insignificant and enteric protein loss has been suggested as the cause. A case with supportive evidence for this is reported.

The relationship between serum viscosity, hypervolaemia and clinical manifestations associated with circulating paraprotein

In 44 of 56 patients with malignant paraproteinaemia the relationship of serum viscosity, plasma volume (PV), estimated blood volume (BV) and clinical findings was investigated and in the remaining 12 patients one or more of these parameters was studied. There was a correlation between increased PV and serum viscosity (r = 0.66, P less than 0.001). The retinopathy characteristic of the hyperviscosity syndrome (HVS) was always associated with serum viscosity greater than or equal to 3.8 and with hypervolaemia. The evidence that the retinal changes were related more closely to serum hyperviscosity than to hypervolaemia is twofold. First, there was a considerable overlap in the degree of BV expansion, but not serum hyperviscosity, in patients with and without retinopathy. Second, the retinopathy in a patient with Waldenström's macroglobulinaemia (WM) improved after plasma exchange with little change in BV. While bleeding was often associated with retinopathy seven patients with multiple myeloma (MM) had no retinopathy, viscosities greater than or equal to 4.3 and BV in the same range as patients with no clinical signs. Haemorrhage in such patients may thus be unrelated to the property of the paraprotein responsible for hyperviscosity. Measurements of PV in a patient with WM having repeated plasma exchanges for bleeding suggested that hypervolaemia may contribute to haemorrhage in some patients. It is suggested that the term 'HVS' should be restricted to patients with retinopathy and that hypervolaemia should be considered a characteristic feature of this syndrome.

In vitro stimulation with mitogen and antigen in patients with monoclonal gammopathy

Peripheral blood lymphocytes from 32 patients with defined paraproteinaemia (16 IgG, 9 IgA and 7 IgM) and from 15 healthy donors were studied for their in vitro response to various stimuli, including for unspecific mitogens such as Phytohaemagglutinin (PHA), Pokeweed mitogen (PWM) and Concanavalin A (ConA) as well as specific antigens such as purified Tuberculin, Candida, Varidase, Tetanus Toxoid, Vaccinia antigen and Vaccinia-control antigen. Mitogens and antigens were lyophilized in Microtiter plates. The lymphocytes of all tested patient-groups responded (measured by H3-Thymidin-uptake) significantly lower towards the unspecific mitogens than those of the control group. If the patients' lymphocytes were stimulated by the specific antigens, their in vitro response was significantly diminished to candida and vaccinia. Macroglobulinaemia showed significantly lower response to ConA if compared to myelomas of IgG- and IgA-type. No correlation was found between mitogen and antigen response and the serum concentration of the paraproteins or immunoglobulins. The results show that monoclonal gammopathy and especially macroglobulinaemia are associated with abnormalities of the cellular immunity which correlates with the clinical observation of increased fungal and viral infections.

Autoradiographic study of the permeability characteristics of the small intestine

This autoradiographic study demonstrates the distribution of a range of small solutes and macromolecules in the mucosa of the guinea-pig small intestine after intracardiac injection. The substances investigated were: 14C-urea, 3H-mannose, 3H-inulin, and 125I polyvinylpyrrolidone (PVP). Small bowel biopsies were taken at intervals from one to 60 minutes after injection and the tissues processed for autoradiography. Light microscopic examination of the autoradiographs showed that the compartmental distribution depended on the molecular size of the substances being studied. Urea and mannose, as small solutes, were uniformly distributed throughout the intravascular, extravascular, and epithelial compartments. Inulin was evenly distributed in the vessel lumen and extravascular space but there was a considerable drop in concentration in the epithelium. PVP exhibited the most marked gradients, the concentration being greatest in the vascular lumina, lower in the extravascular space, least in the epithelium. Thus there appear to be two barriers to macromolecular passage which are freely permeable to small solutes: the capillary wall and the epithelium. At a light microscopical level it is not possible to observe whether the limiting membrane of each of these barriers is the cell plasmalemmal membrane or the basement membrane. The selectivity of the epithelial barrier is greater than that of the capillary barrier.

Persistence of immunoglobulin G and immunoglobulin M antibodies after postnatal rubella infection determined by solid-phase radioimmunoassay

The appearance and persistence of immunoglobulin M (IgM) and IgG antibodies in postnatal rubella infections were studied by employing a solid-phase radioimmunoassay test. Altogether, 222 serial serum specimens from 51 patients with acute rubella infection were tested. Both IgG and IgM antibodies developed rapidly and appeared in all patients within 4 days after the onset of rash. In some patients, the IgM antibodies clearly preceded the IgG antibodies; however, the reverse situation was also noticed in a few cases. The IgG antibodies showed only minor changes after 8 to 10 days from the onset of rash. The IgM titers also reached a maximum level at approximately 8 to 10 days after the onset of rash, after which time a rapid decrease was normally seen. The mean half-life of IgM antibodies after 15 days from the onset of rash was 4.5 days, giving for IgM antibodies persistence times from 43 to approximately 80 days. Two patients with a prolonged IgM antibody response were detected. One of these patients had bilateral arthritis of the knee as a complication, whereas in the other patient no complication caused by rubella virus was detected. The IgM antibody response and its value in diagnosis are discussed.

Stimulation by acidic phospholipids of protein-catalyzed phosphatidylcholine transfer

1. The catalyzed transfer of phosphatidylcholine from unilamellar liposomes to mitochondria by phospholipids exchange protein from beef heart or from beef liver is stimulated by the presence of up to 20 mol% acidic phospholipid (phosphatidylinositol or phosphatidic acid) in the liposome. Co-sedimentation of liposomes with mitochondria increases with increasing mol% acidic phospholipid. 2. The catalyzed transfer of phosphatidylcholine from unilamellar liposomes to multilamellar vesicles by beef heart or beef liver exchange proteins is also stimulated by the presence of acidic phospholipid. No co-sedimentation of negatively charged transfer of phosphatidylcholine from multilamellar vesicles to unilamellar liposomes by phospholipid exchange protein from beef heart or beef liver reaches a maximum at 7.5% phosphatidylinositol in the liposomes. Inhibition of phosphatidylcholine transfer was observed at levels of liposome phosphatiylinositol of greater than 15 mol% only in the presence of beef liver exchange protein. 4. Changes in the surface charge of liposomes by the addition of acidic phospholipid were verified by a novel application of polyvinylchloride block electrophoresis that allows the direct measurement of the relative electrophoretic mobility of sonicated vesicles.

Small intestinal permeability. 1. Effects of ischaemia and exposure to acetyl salicylate

Permeability of the small intestinal mucosa was estimated using a perfusion technique after either a period of ischaemia or exposure to acetyl salicylate. It was shown that these procedures increased the passive permeability of the mucosa to macromolecules while maintaining normal mucosal selectivity. Histologically, there was derangment of the epithelial cell layer of the villous tips without damage to the epithelial basement membrane or subepithelial structures. It is concluded that the epithelial cell layer is purely limiting with no selective function and that the role of selectivity must be ascribed to either or both of the other mucosal barriers, the capillary and the epithelial basement membrane.

Anti-tumour antibodies in normal mouse sera

Evidence for the involvement of the immune system in surveillance against nascent tumors was sought by testing whether normal mouse sera were cytotoxic in the presence of rabbit complement for a variety of lymphoid and non-lymphoid tumor-cell lines. Tumour-reactive antibodies were detected in all mouse sera tested, including sera from congenitally athymic (nude) mice. Considerable variation was noted, however, in the levels of naturally occurring antibodies against specific tumor antibodies were identified as being predominantly IgM. The possible relevance of natural anti-tumor antibodies to immune surveilance was discussed.

The number and morphology of trypanosomes in the blood and lymph of rats infected with Trypanosoma brucei and T. congolense

The thoracic lymph duct of rats infected with Trypanosoma brucei and with T. congolense was cannulated at different stages of infection. Trypanosomes were always present in the lymph of rats infected with T. brucei, wheras they were absent or very scarce in the lymph of rats infected with T. congolense. There were greater fluctuations in the numbers of trypanosomes in the blood than in the lymph. The intra- and extravascular populations of T. brucei differed: stumpy forms were present only in blood; dividing forms were usually more numerous in lymph.

Canine lipoproteins and atherosclerosis. II. Characterization of the plasma lipoproteins associated with atherogenic and nonatherogenic hyperlipidemia

Characterization of the hyperlipoproteinemia induced by feeding high-cholesterol diets to hypothyroid dogs was undertaken in an attempt to identify a lipoprotein pattern or a specific lipoprotein responsible for the atherosclerosis associated with such hyperlipoproteinemia. Various degrees of hyperlipidemia and atherosclerosis were produced during the diet, which was imposed for 3 months to more than a year. Dogs referred to as hyporesponders did not develop significant atherosclerosis despite plasma cholesterol levels ranging from two to five times normal or up to 750 mg/100 ml. This nonatherogenic hyperlipidemia was characterized by an increase in the LDL (low density lipoprotein) and HDL c classes (HDL c refers to a broad spectrum of cholesterol-enriched particles which resemble high density lipoproteins). Dogs referred to as hyperresponders developed significant and often complicated atherosclerosis. Their plasma cholesterol levels were in excess of 750 mg/100 ml, and most of the increased cholesterol was present in lipoproteins with density less than 1.006 g/ml. Several classes of lipoproteins were isolated by ultracentrifugation and purified by Geon-Pevikon block electrophoresis. These lipoproteins were characterized with respect to chemical composition, electrophoretic mobility, immunochemical reactivity, electron microscopic size after negative staining, and apoprotein content as determined by polyacrylamide gel electrophoresis. We concluded that the atherogenic hyperlipidemia of the hyperresponders was characterized by an increase in the amount of cholesterol-rich HDL c as in the hyporesponders but was distinguished by the appearance of a spectrum of cholesterol-rich lipoproteins in the fraction with a density less than 1.006 g/ml. One of these cholesterol-rich lipoproteins had the properties of β very low density lipoproteins, and the others had those of HDL c . We suggest that the spectrum of lipoproteins with density less than 1.006 g/ml represents "remnants" that accumulate because of defective catabolism of lipoproteins synthesized to carry excess of dietary cholesterol.