A. W. L. Van Den Wall Bake

Humoral immune response to influenza vaccination in patients with primary immunoglobulin A nephropathy. An analysis of isotype distribution and size of the influenza-specific antibodies.

Primary IgA nephropathy (IgAN) is characterized by mesangial deposits of IgA1, increased serum IgA1 levels, and circulating immune complexes containing predominantly IgA1. It has previously been found that patients with IgAN have a higher than normal IgA response to vaccination, but the IgA subclasses have not been studied. To investigate whether the IgA hyperresponsiveness is limited to the subclass IgA1, which is involved in the pathogenesis of IgAN, we compared the immune responses of 18 patients with 22 healthy controls after intramuscular vaccination with inactivated influenza virus. Antibody titers were significantly higher (P less than 0.0001) for the IgA1 subclass in patients versus controls, but not for the other isotypes. A substantial portion of the IgA and IgA1 antiinfluenza immune response comprised polymers in both patients and controls. There was no preferential response of polymers in patients. Patients produced significantly more monomeric IgA1 antibodies than controls. These results show that patients with IgAN have a hyperresponsiveness limited to the subclass IgA1 and mainly expressed by an excess of monomers.

Serum IgA and the Production of IgA by Peripheral Blood and Bone Marrow Lymphocytes in Patients With Primary IgA Nephropathy: Evidence for the Bone Marrow as the Source of Mesangial IgA

The origin of the mesangial IgA1 in primary IgA nephropathy (IgAN) is unknown. The bone marrow, the prime production site of plasma IgA in healthy humans, has not been previously investigated in patients with IgAN. In patients with IgAN, we found an increased percentage of IgA plasma cells containing IgA1 in the bone marrow (89.7% +/- 2.6% v 84.3% +/- 6.6%, P = 0.01), an increased percentage of serum IgA as IgA1 (92.2% +/- 4.9% v 80.2% +/- 6.6%, P less than 0.001), and an increased percentage of IgA1 of the IgA produced by peripheral blood lymphocytes in culture (75% +/- 16% v 54% +/- 19%, P less than 0.01). These findings are compatible with the bone marrow as production site of the mesangial IgA1. The data on IgA1 polymers are more difficult to interpret because their role in the pathogenesis of IgAN is still controversial. We found an increased concentration of both polymeric and monomeric IgA1 in the sera and supernatants of cultures of bone marrow of patients, although the ratio of polymeric to total IgA1 remained normal. In our opinion, the mucosa of the digestive tract is an unlikely source of the mesangial IgA because the absence of IgA2 in the deposits contrasts to the high percentage of IgA2 plasma cells in the intestinal mucosae. Moreover, in normal individuals, the digestive mucosae contribute very little to plasma IgA. Although the respiratory tract contains a higher percentage of IgA1 plasma cells, the 25% fraction of IgA plasma cells containing IgA2 is still very substantial. This percentage argues against the respiratory mucosae as a source of the mesangial IgA.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunoglobulin A subclass measurement in serum and saliva: sensitivity of detection of dimeric IgA2 in ELISA depends on the antibody used

The existence of two IgA subclasses in humans has been reliably shown by biochemical, immunochemical and genetic means. IgA is unique among immunoglobulins in the regular occurrence of both monomeric and polymeric forms. In order to be able to study the relationship between monomeric and polymeric IgA1 and IgA2 concentrations in the circulation and mucosal compartment i.e. secretions, it is essential that the methods used are not biased by the molecular size of the IgA under investigation. We validated IgA and IgA subclass measurements in serum and saliva by sandwich enzyme-linked immunosorbent assay (ELISA). Coating reagents were specific mAbs against IgA (clone 4E8), IgA1 (clone 69-11.4) or IgA2 (clone 16-512-H5 and clone IF8.58). Pooled normal human serum and purified dimeric IgA1 (d-IgA1) or IgA2 (d-IgA2) myeloma proteins were used to standardize the assays. Polymeric and monomeric forms of IgA in sera from volunteers and patients with myelomatosis were assayed in fractions separated by high performance liquid chromatography (HPLC). Dithioerythritol (DTE) was used to determine the influence of the quarternary structure of IgA on its detection by mAbs. We found that mAbs 4E8, 69-11.4 and 16-512-H5 reliably measured d-IgA, d-IgA1 and d-IgA2 respectively, independent of the standard employed. Clone IF8.58 underestimated the concentration of d-IgA2 (correction factor +/- 2) with increased sensitivity in the presence of DTE. This difference is probably explained by the composition of the immunogen against which the mAb was raised. We conclude that no reliable conclusions can be made concerning the subclass ratio in biological fluids unless the monoclonal antibodies used have been appropriately validated.

Composition of IgA-Containing Circulating Immune Complexes in IgA Nephropathy

Macromolecular IgA is found with a relatively high frequency in the sera of patients with IgA nephropathy (IgAN). This macromolecular IgA consists of polymeric IgA, IgA-containing immune complexes, or both. The presence of polymeric IgA antibodies reflects a recent IgA response. Vaccination data in patients with IgAN suggest that these patients respond more vigorously with their mucosal immune system than do controls. The association of exacerbations with upper respiratory tract infections suggests that the immunogenic stimuli probably are of microbial origin and are presented to mucosal surfaces. Analysis by sucrose density ultracentrifugation has shown that the macromolecular IgA may contain IgG, IgA rheumatoid factor, and C3. The search for the antigen or antigens specifically responsible for IgAN has been unsuccessful. Although IgG and IgA rheumatoid factor may contribute, they do not account for the pathogenesis of the disease in all patients. Alternative mechanisms have to be assumed for patients who do not have detectable levels of IgA-containing immune complexes. They could have polymeric IgA or IgA-containing immune complexes intermittently, as has been shown in children with relapsing IgAN. The binding of circulating IgA antibodies to antigens present in the mesangium can lead to the local formation of deposits in the absence of circulating IgA complexes.

Secretory immunoglobulin A (IgA) responses in IgA nephropathy patients after mucosal immunization, as part of a polymeric IgA response

Secretory immunoglobulin A (SIgA), although generated at mucosal surfaces, is also found in low concentrations in the circulation. Recently, SIgA was demonstrated in mesangial deposits of patients with immunoglobulin A nephropathy (IgAN), suggesting a role in the pathogenesis. This finding is in line with the belief that high molecular weight (HMW) immunoglobulin A (IgA) is deposited in the kidney. However, there is little information on the size distribution of antigen‐specific IgA in circulation upon mucosal challenge. In this study we measured antigen‐specific IgA, including SIgA, in serum following challenge of IgAN patients and controls via intranasal vaccination with a neoantigen, cholera toxin subunit B (CTB). We size‐fractionated serum and nasal washes to study the size distribution of total IgA, SIgA and CTB‐specific IgA. Finally, we compared the size distribution of antigen‐specific IgA after mucosal immunization with the distribution upon systemic immunization. A significant induction of antigen‐specific SIgA was detectable in serum of both patients with IgAN and controls after mucosal immunization with CTB. Independent of the route of immunization, in both groups the antigen‐specific IgA response was predominantly in the polymeric IgA fractions. This is in contrast to total IgA levels in serum that are predominantly monomeric. We conclude that mucosal challenge results in antigen‐specific SIgA in the circulation, and that the antigen‐specific IgA response in both IgAN patients and in controls is of predominantly HMW in nature. No differences between IgAN patients and controls were detected, suggesting that the size distribution of antigen‐specific IgA in the circulation is not disturbed specifically in IgAN patients.

Interaction of IgA with Complement and Phagocytes

Abstract Immununoglobulin A (IgA) is found in deposits in organs such as kidneys and skin and may be responsible for local inflammation. The mechanism by which IgA induces inflammation are not clear. The present study summarizes the various properties of human and rat IgA in activation of inflammatory mediator systems such as complement. It is described that human IgA in aggregated state is able to activate the human complement system. In the rat model IgA monoclonal antibodies against dinitrophenol were used to determine the potential of rat IgA in activating the rat complement system. We have found that monoclonal dimeric and polymeric rat IgA are able to activate the rat complement system in an efficient way via the alternative pathway. In addition to the potential of both human- and rat IgA to activate the complement sequence we have also found evidence that large sized soluble aggregates of IgA are able to activate polymorphonuclear leukocytes. S. Aureus opsonized with IgA are also phagocytozed by polymorphonuclear leukocytes The results, combined with our recent observations that increased production of IgA may occur in patients with IgA nephropathy may explain some of the inflammatory processes which are found in patients with deposits of IgA in organs such as kidneys and skin