Biochemical aspects of immune complex formation and immune complex diseases

TRYBE®: an Fc-free antibody format with three monovalent targeting arms engineered for long in vivo half-life

TrYbe® is an Fc-free therapeutic antibody format, capable of engaging up to three targets simultaneously, with long in vivo half-life conferred by albumin binding. This format is shown by small-angle X-ray scattering to be conformationally flexible with favorable 'reach' properties. We demonstrate the format's broad functionality by co-targeting of soluble and cell surface antigens. The benefit of monovalent target binding is illustrated by the lack of formation of large immune complexes when co-targeting multivalent antigens. TrYbes® are manufactured using standard mammalian cell culture and protein A affinity capture processes. TrYbes® have been formulated at high concentrations and have favorable drug-like properties, including stability, solubility, and low viscosity. The unique functionality and inherent developability of the TrYbe® makes it a promising multi-specific antibody fragment format for antibody therapy.

Diverse contributions of avidity to the broad neutralization of Dengue virus by antibodies targeting the E dimer epitope

Antibodies (Abs) recognizing the Dengue virus (DENV) E dimer epitope (EDE) that potently neutralize all DENV serotypes are promising templates for vaccine design. As an important feature for some Abs is their bivalency, we sought to define the role avidity plays in neutralization by EDE Abs. We compared neutralization activity between bivalent IgGs and monovalent Ab fragments (Fabs) for two EDE Abs, A11 and C10. IgG forms of both Abs exhibited more potent neutralization activity than their counterpart Fabs, yet only for C10 was this enhanced activity associated with bivalent binding. A11 and C10 also exhibited differential binding profiles to DENV virus-like particles under acidic conditions mimicking the environment that triggers viral membrane fusion, suggesting that EDE Abs employ diverse neutralization mechanisms despite sharing an epitope. Delineating the full range of Ab binding modes and neutralization mechanisms against a single epitope may inform therapeutic approaches and refine vaccine design.

Delivery route determines the presence of immune complexes on umbilical cord erythrocytes

OBJECTIVE

Umbilical cord blood offers a unique opportunity to study the basal level of immunoglobulin complexes. This study aims to determine the presence of immune complexes and complement deposition on erythrocytes from umbilical cord blood from normal, full-term pregnancies.

METHODS

In vitro pre-formed IgA, IgG, and IgM complexes were used as positive control for flow cytometry detection, and for C3d deposition. Blood samples (34) of umbilical cord blood taken from vaginal and cesarean deliveries were tested for the presence of immunoglobulin complexes.

RESULTS

Fourteen samples from vaginal deliveries and 20 samples from cesarean deliveries were assessed. IgG and IgM complexes were detected on erythrocytes, whereas no IgA complexes or complement deposition was observed. Interestingly, the percentage of IgG complexes was higher on erythrocytes from vaginal delivery samples compared to those from cesarean deliveries. No other associations between immune complexes and other maternal or newborn variables were found.

CONCLUSIONS

IgG and IgM complexes seem to be normally present on umbilical cord erythrocytes. Erythrocytes from vaginal deliveries have a higher percentage of IgG complexes present compared to that from cesarean deliveries. Since no C3d activity was detected, these complexes are non-pathological and should be part of the newborn's initial innate immune response.

Unraveling the immunopathogenesis of glomerular disease

Immune-mediated damage to glomerular structures is largely responsible for the pathology associated with the majority of glomerular diseases. Therefore, a detailed understanding of the basic immune mechanisms responsible for glomerular damage is needed to inform the design of novel intervention strategies. Glomerular injury of immune origin is complex and involves both inflammatory and non-inflammatory processes driven by elements of the innate and adaptive immune system. This review summarizes the basic immune mechanisms that cause glomerular injury leading to the nephritic and nephrotic syndromes. A major focus of the review is to highlight the mechanisms by which antibodies cause glomerular injury through their interactions with glomerular cells, complement proteins, phagocytes bearing complement and Fcγ receptors, and dendritic cells expressing the neonatal receptor for IgG, FcRn.

Glomerulitis induced by cationized bovine serum albumin in the rat

The effects of injected native and cationized bovine serum albumin (BSA- and BSA+ respectively) were evaluated in rats which subsequently received anti-BSA. Thrombocytopenia, low creatinine clearance (Ccr), increased proteinuria, capillary swelling, mild tuft necrosis and BSA+ deposits in glomeruli resulted within 24 h of BSA+ injection. Later BSA+ produced mesangial expansion glomerular capillary wall (GCW) thickening and deposits of BSA+ accompanied by rabbit anti-BSA and rat anti-BSA which correlated well with small mesangial, subendothelial and subepithelial electron-dense granular accumuli. These latter enlarged considerably after the injection of anti-BSA. BSA- controls showed minimal or no lesions. The disappearance from the blood (t1/2) of a single dose of immune complexes (IC) prepared with chromatography-purified, radioiodinated anti-BSA - BSA- and BSA+ was determined in another group of rats. The t1/2 of BSA- anti-BSA was 42.8 h (95% confidence: 39.8-46.2) while that of BSA+ anti-BSA was 52.5 h (48.1-57.8). These results suggested that serum sickness glomerulitis developed only in rats injected with BSA+, due to in situ IC which presumably grew by accretion of foreign anti-BSA. Circulating IC may have developed and colocated with the latter, with dissociation and recombination at these sites. It is postulated that the functional-immunomorphological changes and the slow removal of cationized IC reported herein could be explained by the highly positive net charge of the injected antigen.

Passage of undegraded dietary antigen into the blood of healthy adults. Further characterization of the kinetics of uptake and the size distribution of the antigen

The molecular weight distribution of ovalbumin (OA) absorbed into the blood in eight healthy adults after a test meal was analysed by high pressure liquid gel permeation chromatography (HPLC) followed by ELISA for OA. OA was found either as free OA or as aggregates of a size mainly below 700 kD. The addition of OA in vitro to an antibody-containing serum resulted in OA-containing immune complexes (OA-IC) of similar size. The size distribution of serum OA-IC was more heterogeneous late than early in the 7-h observation period. Free OA disappeared at an equal or higher rate than OA-IC when both entities were present in the same individual. The presence of OA-IC was related to the serum IgG antibody levels. IgG, but not IgA or IgM, could be detected in OA-IC (in three individuals) by ELISA. The kinetics of OA appearance was followed for 48 h after a test meal in three individuals. In one person, serum OA reached peak values at 24 h and detectable amounts persisted for 48 h after the test meal. In the other test persons the OA levels peaked earlier. The present study indicates that in healthy adults dietary antigens are absorbed and circulate regularly in minute amounts apparently as native protein and/or as small immune complexes, mostly containing IgG antibodies.

Immune-induced vascular connective tissue alterations in rabbits chronically immunized with bovine serum albumin: biochemical studies on collagen, glycosaminoglycans, RNA, and DNA in normal and injured aorta

Repeated intravenous injections of bovine serum albumin in rabbits caused a significant reduction in the aortic in vivo biosynthesis of chondroitin-4,6-sulfate, whereas no changes were observed in the synthesis of other glycosaminoglycans nor in the content of collagen. This contrasts the biochemical changes generally seen in acute vascular injury. When experimentally elicited vascular injury and repair processes were induced in chronically immunized rabbits, the proliferative response was greatly inhibited, as reflected by a significant diminution of the DNA amount. Also, the vascular connective tissue matrix repair was restrained: the aortic content of collagen and the collagen type III/I ratio was repressed, and the in vivo biosynthesis of sulfated glycosaminoglycans was markedly reduced. All immunized rabbits developed antibodies to bovine albumin, but in only a few were circulating immune complexes detected. The inhibitory effect of persistent immunostimulation on the nonspecific processes of repair in vascular connective tissue may be of significance as to chronicity of vasculitis, as well as inflammation and repair in general, in inflammatory connective tissue diseases.

Isopycnic ultracentrifugation of immune complexes

Isopycnic ultracentrifugation is frequently applied for preparative isolation of macromolecules. Using bovine serum albumin (BSA)-anti-BSA antibody complexes as a model system, isopycnic banding of complexes was observed in CsCl, Nycodenz, and sucrose gradients. In CsCl gradients, free antigen or antibody could not be separated from the immune complexes. Variations in antigen to antibody ratio from equivalence and in the amount of complement present during complex formation resulted in zone broadening and banding at slightly lower densities in Nycodenz. This was not observed in sucrose. Serum immune complexes were isolated from patients with rheumatoid arthritis or ankylosing spondylitis. Banding of in vivo-formed immune complexes was observed more frequently in sucrose than in Nycodenz.

Circulating immune complexes in chronic myeloid leukemia: turbidimetric measurement and two-dimensional electrophoretic analysis

A 3.75% polyethylene glycol -6000 mediated turbidimetric method was used for the estimation of levels of circulating immune complexes (CIC) in sera of normal human subjects and patients with chronic myeloid leukemia (CML). In terms of equivalents of heat-aggregated gamma globulin (eq.HAGG mg/ml serum), the mean levels of CIC were: 5.69 mg/ml (SD 4.78) in 81 normal human subjects; 22.63 mg/ml (SD 9.86) in 52 untreated CML patients; 7.61 mg/ml (SD 5.74) in 54 CML patients in remission; and 21.70 mg/ml (SD 8.15) in 18 CML patients in relapse. High CIC levels, thus, showed a significant association with the pretreatment -- and relapse -- status of the disease (p less than 0.001 and p less than 0.001, respectively). Though the levels decreased during remission, they were still significantly above the mean level in the controls (p less than 0.05). The CIC level-disease status relationship was clearly evident in the serial studies on 19 CML patients who donated serum samples prior to treatment as well as during remission. Two-dimensional electrophoretic analysis of the CIC samples revealed the presence of a polypeptide (mol. wt approx. 37,000 and pI approx. 5.8) in 10 out of 18 CIC samples from the untreated CML patients. Such a moiety was not detected in six CIC samples from normal subjects. The association of this polypeptide with CML gains support from the observation that in 5 CML patients, this moiety was present in the CIC samples obtained prior to treatment but absent in the samples subsequently obtained during remission.

Determination of affinity of monoclonal antibodies against human IgG

A method for determining the affinity and the concentration of mouse monoclonal antibodies against human IgG has been developed. The method comprises two steps. First, monoclonal antibodies are allowed to combine with radioiodinated human IgG. Secondly, mouse monoclonal IgG with and without complexed IgG is precipitated with rabbit IgG against mouse IgG. As the antigen is divalent complexes of varying composition are formed in this system leading to deviations from linearity in plots obtained in commonly employed analytical systems. The theoretical background of these systems has been studied by computer stimulation, and a concentration effect on the formation of immune complexes were demonstrated. The affinities (in terms of the association constants (of 6 monoclonal antibodies were estimated and found to be in the range from 2 X 10(6) M-1 to 5 X 10(8) M-1.

Polyclonal B cell activation in the acute phase of systemic lupus erythematosus--aspects of pathogenic significance

B lymphocytes from patients suffering from systemic lupus erythematosus show increasing rates of spontaneous transformation in prolonged cultivation (144 hr). An additional B cell stimulation could be detected following the addition of sera from lupus erythematosus patients (isolated during the acute phase of disease) to the culture medium. In addition enriched mitogenic serum components from lupus sera increase the 3H-thymidine uptake of Brucella abortus primed B cells of healthy controls. The incorporation of 3H-thymidine with respect to the Brucella antigen concentration is described.